What should she do about her sister who is threatening suicide if she doesn't marry a man who is intermittent in prayer, and about her mother who will fall ill because of sending her furniture there?

It is advisable to counsel the man regarding his negligence in prayer and to explain the gravity of this matter. If he persists in his state, then the sister should be advised to marry someone whose religion and character she approves of; otherwise, there is no religious impediment to her marrying him. If the mother objects to this marriage due to the man's negligence in prayer, the general principle is to obey the mother, unless there is a fear of harm befalling her by not marrying him due to her strong attachment to him. It is important to emphasize the danger of suicide.