Well, a lot of this depends upon your current home value and the lien owed on it.
Have you refinanced it in the last few years?
To your knowledge, is your home currently in a declining market?
If it is then you may have trouble obtaining the value that you want.
To find answers to that question, maybe the best thing to do would be to contact an appraiser and ask that question. They can easily find an approximate value for you over the phone.
In regards to the purchase, things would be a lot more flexible with a purchase in a declining market. This is a buyers market. Don't let anyone say differently to you.
What type of loan you get really depends upon whether or not you sell your present home first.
Your wife's income can also be used, SS disability, definitely a verifiable source of income. To use her income, she would also need to be on the loan.
I provide competitive national prime lending, and your credit score definitely fits into that category. You are welcome to call me directly 510.776.5875.