Of course you have proof, your parents can write a letter explaining that they received "X" amount of money every month from you guys for the past 2.5 years ( it could be any amount that you normally take out from your bank account). If this letter can not help you, look for a mortgage broker not for a loan officer from any bank to assist you with your loan. Mortgage brokers have access to many banks, private lenders and many different programs.
Best of Luck,
Century 21 tenace