Unless you allow the existing home to fall into foreclosure that you own after you purchase another home, the lender on your first home most likely will not see anything fraudulent as to the purchase of the second home especially if you need to move due to your son's health.I suggest that you consult with an attorney or a real estate agent as to what can be done to rent out the home that you want to move from. My experience is that every home is rentable. The issue is usually at what monthly rent and what length of the lease. If there is a college near where you live, you should have no problem being able to rent out the home to students.