Firstly: 

These actions of the person you are asking about sitting with constitute kufr and apostasy, and we are amazed that he claims to be a Muslim when this is the case. Not praying is major kufr, as is proven in the Qur’aan and Sunnah and by the consensus of the Sahaabah (may Allaah be pleased with them). 

With regard to women’s hijab, if what is meant is covering the face (niqaab), there is a difference of opinion among the scholars concerning it. The more correct view is that it is obligatory for all women and that it does not apply only to the wives of the Prophet (peace and blessings of Allaah be upon him).  

Shaykh Saalih ibn Fawzaan al-Fawzaan (may Allaah preserve him) said:   

With regard to niqaab, covering the face is obligatory, according to the correct scholarly opinion, and this is what is supported by the saheeh evidence, because Allaah says (interpretation of the meaning): 

“and to draw their veils all over Juyoobihinna (i.e. their bodies, faces, necks and bosoms)”

[al-Noor 24:31]. 

And Allaah said concerning the wives of the Prophet (peace and blessings of Allaah be upon him) (interpretation of the meaning):

“And when you ask (his wives) for anything you want, ask them from behind a screen, that is purer for your hearts and for their hearts”

[al-Ahzaab 33:53]. 

The fact that it is speaking of the wives of the Prophet (peace and blessings of Allaah be upon him) does not mean that the ruling should not apply to other Muslim women, because the reason for that is general, namely “that is purer for your hearts and for their hearts.” 

So the reason is general and applies both to the wives of the Prophet (peace and blessings of Allaah be upon him) and to other women. Purity is required of all, because Allaah says in another verse (interpretation of the meaning): 

“O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies (i.e. screen themselves completely except the eyes or one eye to see the way). That will be better, that they should be known (as free respectable women) so as not to be annoyed”

[al-Ahzaab 33:59]. 

End quote from Fataawa al-Shaykh al-Fawzaan (4/242, 243; question no. 250). 

For more information please see the answer to question no. 11774. 

But if what is meant by hijab is covering the head, then there is no difference of opinion among the scholars concerning the fact that it is obligatory. His rejection of both types, and his making fun of them, is apostasy from Islam, because even though covering the face is not obligatory according to some scholars, they are unanimously agreed that it is prescribed in Islam and that it is part of the religion of Allaah, so denying it and making fun of it is kufr which puts one beyond the pale of Islam. 

There is no excuse at all for this heretic to make fun of the Mother of the Believers ‘Aa’ishah (may Allaah be pleased with her), rather it is indicative of what is in his heart of hypocrisy and heresy, which shows itself in this slip of the tongue. ‘Aa’ishah is the Mother of the Believers and the wife of the Prophet (peace and blessings of Allaah be upon him), whose innocence was declared by Allaah in verses that will be recited until the Day of Resurrection. The one who makes fun of her is in fact making fun of her husband, who is the Prophet (peace and blessings of Allaah be upon him), and the one who denies that she is the Mother of the believers is putting himself outside of their circle, but he does not harm her at all. 

Secondly: 

If this is the case with this relative, then he should be told that he is doing something which implies that he is an apostate, and that he must repent and come back to his religion. If he meets his Lord in this state, he will not be meeting Him as a Muslim. 

What you must do – after advising him – is shun his company and beware of him, unless the one who wants to sit with him has a sufficient level of knowledge to repel his kufr. His companions should beware of his evil, and upholding ties of kinship with him is not obligatory, rather it is not permissible to initiate the greeting of salaam with him. 

Allaah says (interpretation of the meaning): 

“And when they hear Al‑Laghw (dirty, false, evil vain talk), they withdraw from it and say: ‘To us our deeds, and to you your deeds. Peace be to you. We seek not (the way of) the ignorant’”

[al-Qasas 28:55].

Shaykh ‘Abd al-Rahmaan al-Sa’di (may Allaah have mercy on him) said: 

“And when they hear Al‑Laghw (dirty, false, evil vain talk)” from an ignorant person who addresses it to them, “they say” – the words of the slaves of the Most Merciful who have understanding – “To us our deeds, and to you your deeds” i.e., each will be requited for his deeds that he did by himself, and he will not bear anything of the burden of another. This implies that they are innocent of what the ignorant do of laghw (vain talk), falsehood and idle talk. 

“Peace be to you” i.e., you will not hear anything from us but good, and we will not address you as your ignorance deserves. Even if you allow yourselves to indulge in this rotten talk, we declare ourselves to be above it and we protect ourselves from indulging in it. “We seek not (the way of) the ignorant’” in any sense. 

Tafseer al-Sa’di (p. 620). 

The scholars of the Standing Committee were asked: 

Is it permissible for me to sit with one who does not pray? 

They replied: 

The one who does not pray deliberately and denies that it is obligatory is a kaafir, according to scholarly consensus. If he does not pray because he is heedless and lazy, then he is a kaafir, according to the correct scholarly opinion. Based on that, it is not permissible to sit with these people, rather they should be shunned and cut off, after explaining to them that not praying is kufr, if they are the type of people who may be unaware of the ruling. It is narrated in a saheeh report from the Messenger of Allaah (peace and blessings of Allaah be upon him) that he said: “The covenant that stands between us and them is prayer; whoever does not pray is a kaafir.” And it is narrated in another saheeh report that he (peace and blessings of Allaah be upon him) said: “Between a man and kufr and shirk there stands his giving up prayer.” Narrated by Muslim in his Saheeh. This includes both the one who denies that it is obligatory and the one who does not do it out of laziness. 

Shaykh ‘Abd al-‘Azeez ibn Baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan. 

Fataawa al-Lajnah al-Daa’imah (12/374, 375) 

The scholars of the Standing Committee were asked: 

Is it permissible to say salaam to one who does not pray? 

They replied: 

The one who does not pray because he denies it is obligatory is a kaafir according to scholarly consensus, and the one who does not pray out of laziness, but does not deny that it is obligatory is a kaafir, according to the correct scholarly view. So it is not permissible to say salaams to him, or to return his salaam if he greets you with salaam, because he is regarded as an apostate from Islam.  

Shaykh ‘Abd al-‘Azeez ibn Baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan, Shaykh ‘Abd-Allaah ibn Qa’ood. 

Fataawa al-Lajnah al-Daa’imah (24/141, 142) 

The scholars of the Standing Committee said: 

The one who makes fun of the religion of Islam or the Sunnah that is proven from the Messenger of Allaah (peace and blessings of Allaah be upon him), such as letting the beard grow, shortening the clothes to above the ankles or halfway up the calves, when he knows that this is proven, is a kaafir. The one who mocks the Muslim and makes fun of him because of his adhering to Islam, is a kaafir, because Allaah says (interpretation of the meaning): 

“Say: ‘Was it at Allaah ( عز و جل ), and His Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) and His Messenger (صلى الله عليه وسلم) that you were mocking?’

66. Make no excuse; you disbelieved after you had believed”

[al-Tawbah 9:65-66]

Shaykh ‘Abd al-‘Azeez ibn Baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan, Shaykh ‘Abd-Allaah ibn Qa’ood. 

Fataawa al-Lajnah al-Daa’imah (2/43-44). 

Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him) said: 

What you must do is shun the one who does not pray, and cut off ties with him, and do not accept his invitation, until he repents to Allaah from that; but you should also advise him and call him to the truth, and warn him of the consequences of not praying in this world and in the Hereafter, in the hope that he may repent and Allaah may accept his repentance. 

Fataawa al-Shaykh Ibn Baaz (10/266) 

Shaykh Saalih ibn Fawzaan al-Fawzaan (may Allaah preserve him) was asked: 

Is it permissible for me to sit and eat and drink with someone who does not pray and persists in not praying? 

He replied: 

It is not permissible for you to sit with him and eat and drink with him, unless you are advising him and rebuking him, and you hope that Allaah may guide him at your hands. If you are sitting with him, then this is what you must do with him, because this comes under the heading of denouncing evil and calling people to Allaah, and perhaps Allaah may guide him at your hands. 

But if you are sitting with him and eating and drinking with him without denouncing him, and he is persisting in not praying, or is persisting in some major sin, then it is not permissible for you to mix with him. Allaah cursed the Children of Israel for something similar to this. He says (interpretation of the meaning):  

“Those among the Children of Israel who disbelieved were cursed by the tongue of Dawood (David) and ‘Eesa (Jesus), son of Maryam (Mary). That was because they disobeyed (Allaah and the Messengers) and were ever transgressing beyond bounds.

79. They used not to forbid one another from Al-Munkar (wrong, evildoing, sins, polytheism, disbelief) which they committed”

[al-Maa'idah 5:78-79].

In the commentary on this verse it is narrated that one of them would see another committing sin and tell him not to do that, then he would meet him the next day and he would still be persisting in sin, and he would not tell him not to do that and he would mix with him, and would eat and drink with him and sit with him. When Allaah saw that they did that, He set them against one another, and cursed them on the lips of their Prophets. 

And the Prophet of Allaah (peace and blessings of Allaah be upon him) warned us against doing such things, lest there befall us the punishment that befell them. 

End quote from Fataawa al-Shaykh al-Fawzaan (2/246, question no. 215) 

See also the answer to questions no. 4420 and 47425. 

And Allaah knows best.