You can't. The lender will require an arms length transaction and won't allow a related party to be the buyer for a short sale.
Ditto what @Jon Holdman said. You cannot buy a family member's or friend's property in a short sale, which is a legality set up to guard against fraud.
Now if you meant instead that your parents have a contract on a short sale property that you'd like to take over/buy from them, that could be a different animal ... though I still don't think you'd be allowed to do it.
And loans from private lenders are typically much shorter terms, nowhere near 30 years. I believe 1-2 is the norm, though someone else can correct me if I'm wrong. (You might purchase a buy-and-hold using private money, but then you'd refi into a traditional loan.)
Thanks @Jon_Holdman & @Karin_Dimauro.
Well I definitely know now. Appreciate the help