What is the religious ruling concerning children who were undutiful to their deceased father during his lifetime and after his death, and what is incumbent upon the dutiful son to do towards his siblings?

The separation of parents does not permit dereliction of duty towards either of them. Rather, it is obligatory to show filial piety to them and obey them in what is good. The custody of young children belongs to their mother, while older children are given the choice to reside with either parent. Whoever falls short in showing filial piety to one of their parents after their death is sinful. Exaggerated grief or hanging up pictures is not part of filial piety. Legitimate mourning is for three days, and nothing benefits the deceased except supplication and charity. The right of the mother is great and more emphasized than the right of the father.