Fannie & Freddy allow up to 10 properties to be financed. I'd speak to at least two or three different lenders, making sure only one runs your credit report. Having your credit ran (hard pulls) more than 3 things in one week, affects your FICA score.
One problem you have is qualifying for another principle property. You have two options
1) purchasing the new home as an investment property - thus a higher interest rate...
or
2) moving out of the existing property, renting it out. Then short term renting an apartment near where you want to buy another home. That way you can show your next home is going to be a principle property.
The main issue you have is your DTI score being to high....
When you are qualifying for the new loan, you are going to need a "a "Real Estate Owned Schedule" to show your rental income. See link
http://www.winterandcompany.com/form...realestate.xls
Your wife living in the former house and her mother in the home she lives in. Show in your checking account your receiving rental income for both property's. (Using you wife's income). That way you can cancel out those mortgages. Keep in mind most banks only allow only 75% of rent collected, to be used as rental income on a 1003 loan application.
Good Luck