Would God be angry with a son who refuses to relinquish a portion of his inheritance to his brother, based on his mother's request, while his financial circumstances do not allow for it and he is in debt?

You are not religiously obligated to obey your mother in waiving your share of the inheritance for your brother. Obedience to parents is conditioned upon what benefits them and does not harm the child. Jurists have not permitted a parent to take from a child's wealth to give it to another child. If the mother causes a problem, one must be rational and not give Satan an opportunity to cause discord and sever kinship ties. We advise you to be gentle with your mother, manage the situation tactfully, involve good people to persuade her, and treat her kindly as much as possible.