Raquel, First, there is no way for you to buy the property as a short sale; therefore, you would have to bring the difference over the appraised value, minus down payment, to the closing table. For example, house is worth 150K, but value is 100K. FHA loan would require 3.5% (3,500) down payment for a loan amount of 96,500. Your cash to close (plus closing costs) would be 53,500 (down payment and underage of loan payoff). Also, the fact remains that unless you are going to live in the property you are really going to need to put 25% to 30% down...reality check: 25K down payment, plus 50K underage, plus closing costs. If your parents credit is not "horrible" you might consider doing a FHA refinance with you on the loan as a non-occupant co-buyer in lieu of buying the property outright. You would still have to reduce the underage for qualification purposes.
Given the current market it is difficult to encourage someone to put that kind of capital into an asset that is likely not going to be profitable for quite some time. However, I recognize there may be emotional and/or other reasons why you and your parents want to keep the current property. There are ways to do it; however, it would be fairly challenging.
Additonally, if you already own a home you are going to have to qualify for both mortgages. I believe you really need to talk with a mortgage professional to deem if 1). anything is possible and 2). if you reallly want to make the financial commitment. Your goals are extremely noteworthy; however, it may make more sense to start looking at other options.