Depending on his debt ratio alone, it could be used as a compensating factor for approval. Is he trying to buy your home from you as his primary residence? FHA would be a good route to go one that because, even though they have a standard low debt-to-income ratio, an underwriter could use your income as the compensating factor. I actually just closed a purchase loan for my brother who is engaged and it worked well for him. On paper he had a back end 56% DTI but I sent in paystubs for his fiance who was not on the loan (or title) and it helped his approval.