I think I can give a short answer. The underwriting requirements that most banks have in place look for the down payment not to be in the form of debt. If it isn't a form of debt, then that debt gets factored into the overall debt service ratio, and these are the measures that were recently tightened, particularly as they relate to ensured mortgages. Lenders are meant to factor in the source of the down payment and whether or not that source is further debt. Now, whether or not the bank of mom and dad would adjust the interest rate in the same way as conventional lenders is something that's always hard to predict.
