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Unfortunately from your description it sounds like you would be stuck with 5 years. The is an exception for a longer payback period if you are purchasing your primary residence. The problem that I see is that you already own your personal residence. Would obtaining a mortgage in your name be an option. This would give you the option for a 15 year payback and a tax deduction (which may or may not be beneficial for you). If you itemize you would benefit from the mortgage interest and property taxes.
I hope this helps. Please let me know if you have any other questions or need clarification.