What are the legitimate Islamic guidelines and advice for someone who took out an interest-based loan to build a house, and is now suffering from marital problems, disobedient children, and a lack of blessing in their provision?

If the loan involves interest, then it is usury (riba), which is forbidden, and one must repent from it and not return to such a transaction. There is no harm in benefiting from the house built with this loan because the prohibition of the loan is attached to the borrower's responsibility, not to the money itself. Family problems or issues related to salary may be due to the loan or simply a trial, and one must face that with patience. The children's annoyance may be natural, and the spouses should be keen on economizing in living expenses.