What is the duty of children towards their father who neglected his marital duties towards their mother, and will the wife's patience with this deprivation and oppression be rewarded by God?

The Sharia (definition) obligates justice between wives and prohibits preferring one wife over another, as the Prophet, peace and blessings be upon him, said: "Whoever has two wives and inclines to one of them over the other, will come on the Day of Resurrection with his side leaning." And whatever the father's bad character and injustice towards his wife, that does not negate his right to his children's dutifulness and financial support if he needs it, nor does it permit cutting ties with him or mistreating him. Rather, he must be accompanied with kindness. The wife did well by enduring her husband's injustice, and her reward is great, for the Prophet, peace and blessings be upon him, said: "If a woman prays her five (daily prayers), guards her chastity, and obeys her husband, she will enter Paradise from whichever of its gates she wishes." And the outcome of patience and piety is success in this world and the Hereafter.