Is a wife entitled to prevent her husband from spending two nights a week at his mother’s house, or from frequently visiting his married sister?

Islam has affirmed the obligation to honor one's mother and obey her in what is good. If the mother insists on her request, she must be honored, because a wife has no right [to her husband's time] except for one day and one night out of every four nights. As for the wife's refusal to frequently visit your sister, it appears that she is in the right, because excessive visits lead to wasting time and neglecting duties.