My father in law was committed in prostitution and alcoholic because of this my mother in law committed suicide, at this scenario father law asking for forgiveness, and his son and daughter not willing to accept because he is not a trustable person he may not stand his word and he may commit sin in future. Kindly guide us on the right things against my father in law and what I should do now from the Islamic concept and our shariah rule?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If the situation of your father-in-law is as described, then he has committed grave sins. He is in great danger if he does not repent to Allah, The Exalted. He must be advised and reminded of Allah, The Exalted, and His severe punishment were he to die and meet Allah in such a state (without repentance), unless Allah pardons him. You should seek the help of virtuous people, to whom he would most likely listen, to give him advice in this regard.

You did not clarify in the question the nature of the injustice that he committed against his son and daughter that drove them to refuse to forgive him. If what you mean is that they cut their relations with him, for example, because of his disgraceful conduct, and he came to them apologizing and asking for forgiveness, then it is an aspect of the enjoined dutifulness towards him to accept his apology and to seize this opportunity to try to rectify him and do what we underlined above, namely, to give him advice and seek the help of virtuous people whom he trusts or others from his relatives or friends to whom he would most likely listen, along with supplicating Allah, The Exalted, abundantly in his favor.

They should also graciously turn a blind eye to his being not trustworthy and that he might return to committing the sins he used to commit. Rather, it is incumbent to have good expectations of him if he shows repentance and righteous conduct.

If the mother committed suicide because of the conduct of the father, then she had made a big mistake and committed a serious prohibited act. Suicide is a major sin, and stern warnings have been reported against it in the Sunnah. We ask Allah, The Exalted, to confer His Mercy and Forgiveness upon her. We advise her children to show dutifulness to her after her death by supplicating Allah, The Exalted, in her favor, seeking forgiveness for her, spending in charity on her behalf, and the like, in the hope that such deeds would benefit her in her grave and when she stands before Allah, The Exalted, for reckoning.

Allah Knows best.