I think legally there are different processes for giving loans or even gifts. But as far as the institution giving credit, they will check your last 6 months transactions in your account and if everything looks fine they will not bother about anything. So if you want to buy in 6 months deposit the money from your parents to your account right now.

Different institutions may look at different number of months so you should check with your lender how many months bank transaction history they need from you.