Answer:
It is not his principal dwelling, so HPML will not apply unless the parents are also on the loan and the house is their principal dwelling.
1026.35(a) Definitions. For purposes of this section:
(1) "Higher-priced mortgage loan" means a closed-end consumer credit transaction secured by the consumer's principal dwelling with an annual percentage rate that exceeds the average prime offer rate for a comparable transaction as of the date the interest rate is set: