Their father molested them – should they cut him off?
This criminal father who has betrayed his trust should be advised and called to Allaah, and reminded of the meeting with Him, and should be told how evil it is to do this action which contradicts the idea of fatherhood. For the children are part of the man, so how can a man feel desire towards his own children?! Inna Lillaahi wa inna ilayhi raaji’oon (“Truly, to Allaah we belong and truly, to Him we shall return” – said when faced with a calamity).
If advice and reminders are of no use with him, then he must be stopped and punished severely, to deter him and others like him from doing such abhorrent and repulsive acts.
This great evil does not mean that he loses his right to kind treatment and upholding the ties of kinship, so long as there is no danger of falling into any haraam actions.
Allaah has enjoined kind treatment of parents even if they try to make their child ascribe partners to Allaah. 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”
So his children have to treat him kindly and honour him, but they must also be extremely cautious in their dealings with their father. None of them should stay with him on his or her own. If one of his children dies, he has the right of inheritance, like any other father and child.
You should make a lot of du’aa’ for him, praying that he may be guided and enabled to repent, for hearts are held between two of the fingers of the Most Merciful and He turns them however He wills.
And Allaah knows best.