Lots more info is needed to see if this is a good deal. My husband & I are both Realtors in the South Bay (he was born at Inglewood Hospital). My husband has also had his own Appraisal business for 10 years so he's very good at valuation, something a lot of us Realtors need help with. Here's his website http://www.davemonty.com/
If it is a good deal, you could do a "lease option to buy" which can be beneficial to you because you lock in a price to purchase & you have the "option" to buy at that price within a time period. You are not required to go through with the sale if values go down or you decide you don't want the house afterall. The seller however is required to sell to you at the agreed price, even if values go up.
Is it possible for you to do this directly with your parents & not the "friend" that went to the bank already? I'm not sure what the situation is with your parents. Where are they going to live? Could they hang onto the house if they had you paying them rent and then wait to sell until values went up? If they go ahead with the sale, I would at least make sure they are getting fair market value or talk to the bank about doing a loan modification so they can keep their home.