If you don't qualify to do the purchase of the new RC home, I would recommend contacting COVE Financial [(877) 737-5069 / http://www.covefinancial.com/
] to see if they can help you. The COVE Mortgage Alternative Program (MAP) focus on people who due to foreclosure/bad credit/job changes are unable to buy. COVE buys the home you want to buy, you move into it and pay them rent until you can qualify with 5-6 yrs. You are required to finance it within that timeline.
Don't sell your current upside down home at this time...rent it out, you might be able to get close to/if not the full mortgage payment, and if possible keep paying any extra towards the principal that you possibly can.
Then in 2 yrs you can qualify for the purchase of the COVE home, your price stays at the price when you entered into the agreement with them (2014), and can sell your old home that hopefully house values will have improved and your added principal payment will have worked to get you upside-right. If all goes well you may have a some equity and/or can qualify without selling the old home so it can become your investment property to eventually start paying you.
I hope Cove Financial can be your a solution and this plan can help you out! Best of Luck!