Their father treats them and their mother harshly so they have decided to cut him off
Firstly:
The fact that your father does not pray and loves women and pursues them are obvious evils, the most serious of which is his not praying, because not praying is kufr that puts a person beyond the pale of Islam, according to the more correct of the two scholarly opinions. There is a great deal of evidence for that, including the words of the Prophet (peace and blessings of Allaah be upon him): “Between a man and shirk and kufr there stands his giving up prayer.” Narrated by Muslim (82). Hence you have to advise your father and do not despair of his repenting and being guided. You should look for various means of advising him, such as giving him a tape about the rulings on the one who does not pray, and seeking the help of family and relatives who could advise him, and so on.
The fact that he has mistreated you and is still doing so means that you must have compassion towards him in your hearts, for if he were to die and meet his Lord with these deeds, he would meet Him with great sin and disobedience.
Hence you and your siblings and family should look again at your relationship with your father and your attitude towards him. Allaah, may He be glorified and exalted, has commanded us to treat our parents well and to honour them even if they are kuffaar and call us to kufr.
Allaah says (interpretation of the meaning):
“But if they (both) strive with you to make you join in worship with Me others that of which you have no knowledge, then obey them not; but behave with them in the world kindly”
[Luqmaan 31:15]
Ibraaheem (peace be upon him) debated with his mushrik father in a polite manner, as Allaah tells us (interpretation of the meaning):
“And mention in the Book (the Qur’aan) Ibraaheem (Abraham). Verily, he was a man of truth, a Prophet.
42. When he said to his father: ‘O my father! Why do you worship that which hears not, sees not and cannot avail you in anything?
43. ‘O my father! Verily, there has come to me of the knowledge that which came not unto you. So follow me, I will guide you to the Straight Path.
44. ‘O my father! Worship not Shaytaan (Satan). Verily, Shaytaan (Satan) has been a rebel against the Most Gracious (Allaah).
45. “O my father! Verily, I fear lest a torment from the Most Gracious (Allaah) should overtake you, so that you become a companion of Shaytaan (Satan) (in the Hell‑fire).’
46. He (the father) said: ‘Do you reject my gods, O Ibraaheem (Abraham)? If you stop not (this), I will indeed stone you. So get away from me safely (before I punish you).’
47. Ibraaheem (Abraham) said: ‘Peace be on you! I will ask forgiveness of my Lord for you. Verily, He is unto me Ever Most Gracious’”
[Maryam 19:41-47]
Look at the etiquette of this Prophet (peace and blessings of Allaah be upon him), and how he addressed his mushrik father who threatened him. This offers an eloquent lesson for those who are tested with such fathers.
Secondly:
From what we have mentioned it is clear that the father’s rights to honour and good treatment are not waived if he falls shorts and mistreats his family. Rather everyone should fulfil the duties that he owes. So even if he falls short, you should not fall short. Moreover, turning away from him, forsaking him and not serving him will make him even worse, and undoubtedly you do not want that. Many of those who sinned and then repented have spoken of the effect of people’s forsaking them, and said how that made things worse and made them do stupid things that they would not have done if they had felt that they had children who loved them and respected them even though they were harsh and behaved badly.
No matter how bad a person is, he does not forget kind treatment, even if outwardly he appears to be ignoring it. Hence the most beneficial way of dealing with your father is to draw close to him no matter how far away he seems, and to be merciful towards him no matter how harsh he is, whilst also praying that he be guided aright.
Rest assured that your kind treatment will not be wasted before Allaah, and it will bear fruit for you in this world and in the Hereafter, by Allaah’s leave.
We ask Allaah to guide your father and set his affairs and all your affairs straight.
And Allaah knows best.
Wister