Purchasing a home when already on the deed

[Karen Pusateri]

Hello, my parents and I "bought" a home together where my mom took out the mortgage as an investment property and had she, my dad, and myself added to the deed.  I will be actually renting the property while my credit continues to re-establish from a past bankruptcy.  I was advised that in the next 1-2 years my scores should be in a great standing to qualify for a loan myself to assume full ownership of the home.  I have already been advised by my parents they will sell the house to me at the current balance of the mortgage itself. 

My question pertains to the options available for this type of owner transfer in-relation to the mortgage options.  Am I only eligible for a standard sale (ex. they sell to me and I either pay the 20%) or are there other options available, especially ones that would not require a full 20% down?

Thank you!