Firstly: 

One should not sit with people such as these who are in the habit of insulting mothers, unless he has no other choice. He has to express his hatred of their actions and attitude, and to do his best to call them to Islam and advise them, so that they will give up these evil actions. 

If these people are relatives, it is better to strive to uphold ties with them and call them to Allaah, may He be exalted, and to do his utmost in that. If Allaah guides one man at your hands, that is better than red camels (the best kind), and he should not forsake them for his own sake. 

Secondly: 

Anything may be tolerated, except insults to our beloved Messenger (peace and blessings of Allaah be upon him) and slander against his companions and the bearers of his religion. This implies insults against the Lord of the Worlds, may He be glorified, the One Who praised His Prophet (peace and blessings of Allaah be upon him) and chose him, and Who praised his companions and chose them and honoured them with the company of His Prophet (peace and blessings of Allaah be upon him). 

Impugning the honour of the Prophet (peace and blessings of Allaah be upon him) by slandering his wives or one of them, is an insult against him (peace and blessings of Allaah be upon him), because he chose her, kept her and was her companion until he departed this world. And it is an insult against Allaah Who chose her for His Prophet and approved of her as his wife and did not tell him to leave her. 

Such insults can only come from one whose eyes Allaah has blinded to guidance and the true religion, such as the Raafidis and their ilk among the people of misguidance, or those who are influenced by them and have followed their misguidance. We ask Allaah to keep us safe and sound. 

Hence you have to denounce this grave evil, and explain to your family that this is apostasy from Islam, and it is following the path of misguided sinners. You should warn them of bad consequences in this world, let alone the Hereafter. 

If they respond, then praise be to Allaah. If they persist then do all you can to convince them, such as inviting one of the scholars to advise them, even if that is done indirectly, or bringing some books and tapes about this topic. If that does not work with them, then you can cut off ties with them or keep away from them. Do that out of a sense of protective jealousy towards your Beloved (peace and blessings of Allaah be upon him). At the very least you can voice your objections every time they do that, and leave the gathering in that case. 

Al-Baghawi (may Allaah have mercy on him) said, commenting on the hadeeth about Ka’b ibn Maalik and his companions: 

This indicates that the people of bid’ah may be shunned indefinitely. … The Sahaabah, Taabi’een and their followers acted in accordance with that, and the Sunni scholars are unanimously agreed that people of bid’ah are to be shunned. End quote from Sharh al-Sunnah (1/227). 

Ibn Muflih (may Allaah have mercy on him) said: Ahmad said: It is obligatory to shun the one who becomes a kaafir or who commits evil by following bid’ah, or who promotes misguided innovation; this is required of those who are not able to refute it or to speak up against it, or is afraid of being influenced by this. And it was said that he must be shunned altogether, as is the apparent meaning of the words of Imam Ahmad quoted above. Ibn ‘Aqeel stated definitely that this is how it should be, in order to discipline him and bring him to his senses. 

He (i.e., Ibn al-‘Aqeel) also said: If you want to know the state of Islam among the people of this time, do not look at them crowding the doors of the mosques, or how they raise their voices in the Talbiyah. Rather look at how they interact with the enemies of Islam. Ibn al-Rawandi and al-Ma’arri (may the curses of Allaah be upon them) spent their lives writing poetry and prose, and the former said that religion was a myth and al-Ma’arri said that it was false, disbelieving the book of Allaah, may He be glorified and exalted. And they lived for years and their graves were venerated and their books were sold. This indicates that religious commitment has faded from people’s hearts. Something similar was said by Shaykh Taqiy al-Deen ibn Taymiyah (may Allaah have mercy on him). 

Al-Khallaal said: Ismaa’eel ibn Ishaaq al-Thaqafi al-Nisapoori told us that Abu ‘Abd-Allaah was asked about a man who had a Raafidi neighbour who would greet him with salaam. He said: No, and if he greets him he should not return the greeting.  

Al-Qaadi Abu’l-Husayn said in al-Tammaam: There is no difference in the reports concerning the fact that it is obligatory to shun the people of bid’ah and the evildoers among the Muslims, as you can see. The apparent meaning is that there is no difference between the one who openly commits sins and the people of innovation and evildoers. 

He said: No differentiation is made in that regard between a blood relative and a stranger, if it has to do with the rights of Allaah. But if it has to do with the rights of other people, such as slandering, reviling, backbiting, seizing property by force etc, then it depends. If the person to be shunned and the one who did that deed is one of his relatives, it is not permissible to shun him. If he is not a relative, then is it permissible to shun him or not? There are two reports… 

Al-Qaadi said: Ahmad only regarded it as makrooh to shun a relative with regard to one’s own rights because of the reports about upholding the ties of kinship. He regarded it as permissible only with regard to the rights of Allaah, and he disallowed it with regard to the rights of anyone else, according to the report of al-Marwadhi about the rights of a stranger. That is because there is no room for compromise with regard to the rights of Allaah but there is room for compromise when it comes to the rights of human beings. This is explained by the words of the Prophet (peace and blessings of Allaah be upon him): “The debt owed to Allaah is more deserving of being paid off.” 

The views of most of our companions imply that there is no difference. This is the apparent meaning of the words of Imam Ahmad in some places, and it is more appropriate. The reports about upholding the ties of kinship are should be understood in the light of the evidence about shunning. The rights of human beings may be connected to the rights of Allaah, and they are based on ease and forgiving, unlike the rights of human beings.  

End quote from al-Adaab al-Shar’iyyah (1/237-238) 

We ask Allaah to help you and make you steadfast. 

And Allaah knows best.