What is the ruling regarding disobeying a father who divorced the mother a long time ago, did not provide for his children, was harsh towards them, and insulted their mother in front of them? Is it obligatory to obey and honor him despite his shortcomings and his curses upon them, especially since he does not want to do anything for them except for financial compensation?

A father's negligence towards his children does not nullify his right to their dutifulness. Filial piety is one of the most obligatory duties, even if the parents are disbelievers. The children are accountable before Allah for their shortcomings towards their father, and your siblings are committing a forbidden act by speaking ill of their father. Prosperous children must financially support their poor father, his wife, and his young children. We advise the father to repent from his negligence and from verbally abusing the mother. We recall the words of the Prophet, peace and blessings be upon him: "Do not supplicate against yourselves, nor supplicate against your children, nor supplicate against your wealth, lest you coincide with an hour from Allah in which He grants supplications and He answers you."