1) The odds of a lender accepting a transaction involving family members are fairly slim.
2) It's also extremely difficult to get a loan immediately after a short sale because you've already proven that you can't afford the home.
3) CHECK WITH AN ATTORNEY ... BUT ... A lender usually will not touch a transaction where one family member is trying to purchase another family members' property on a short sale, forcing the bank to write off the difference. Both of you trying to do the same to two different lenders could be viewed as the banks as a type of fraud as you're working together to try and write down the others' financial responsibility without paying the full value.
As I said, check with an attorney but odds are this is something you don't want to go near.