Why are a rich wife and sister not obliged to spend on a poor husband
and brother respectively?
Allah has obliged men to spend on their wives and the womenfolk who are under their care, as He says,
Men are the protectors and maintainers of women, because Allâh has made one of them to excel the other, and because they spend (to support them) from their means.
He has decreed that men are the protectors and maintainers of women (Part No. 21; Page No. 157) as He has imbued men with better understanding and due to their spending in mahr and maintenance. In return for their heavier responsibility, men have rights over their wives. A wife should take care of her house and children, and the like. Thus, Allah entitles each of the spouses to have rights befitting their nature as He says:
And they (women) have rights (over their husbands as regards living expenses) similar (to those of their husbands) over them (as regards obedience and respect) according to what is reasonable, but men have a degree (of responsibility) over them. And Allâh is All-Mighty, All-Wise.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.