If parents are financially well-off, is it acceptable for them to insist on monthly financial contributions from their sons, especially knowing that this requirement causes financial hardship for the sons?
When parents are in need, it puts a responsibility on their earning sons to support them. Spending on the parents is obligatory not just recommended. When parents expect financial assistance from their sons, it means that they are in need of that assistance. You can not claim that your parents are well off and don’t need your financial assistance as far as they ask you to assist them. You must do your best to assist them even if you have your own financial challenges. Best place to spend is to assist your parents then your relatives then other needy and deserving persons.
Wassalam.