Is stopping spending on sisters and their father considered disobedience to parents, given that the father intends to disinherit the son, and the son's income is barely enough for his family?

There is a difference of opinion among scholars regarding the obligation of a wealthy brother to support his needy sisters. However, you are not obligated to support them as long as you do not have a surplus beyond your own needs, based on the Prophet's (peace be upon him) saying: "If one of you is poor, let him start with himself. If there is a surplus, then for his dependents. If there is still a surplus, then for his relatives." Nevertheless, you must honor your father, and it is not permissible for you to cut ties with him or treat him badly. It is advisable to continue communicating with your sisters and your aunt, treating them kindly, and helping them to the best of your ability, even if they treat you poorly, in accordance with the Prophet's (peace be upon him) saying: "The one who maintains ties of kinship is not the one who reciprocates, but the one who maintains ties when they are cut off."