It will not be treated as a gift by the IRS if you have formal paperwork including a mortgage (document recorded at the registry of deeds and burnable at the end of the 30 years) to go with the loan note, and also your relative the lender issues 1099 forms every year and enforces non-payment including via foreclosure. However he does not have to join a credit bureau for the purpose of sending them reports on you.
When the "personal" loan is used to purchase your home and secured by a mortgage on said home then the interest you pay is deductible as home mortgage interest.
It should not be callable upon his death.
Upon his death the loan, if not yet paid in full, is still in effect and his estate and then the heirs will receive the monthly payments.
I would suggest that he not do this unless he is in first position; you should pay closing costs so he can engage an attorney to ensure this. Although first position is normally established by which document is recorded first, his attorney should see to it that any other mortgage taken out at the same time specifically declares itself subordinate to his.