FHAs have numerous restrictions, so not sure if a duplex would even qualify. Why don't you get in touch with a mortgage lender and try to get prequalified to find out.
Honestly though, I'd be surpised if you'd be qualified for that much on your income. Keep in mind, you'll have to pay mortgage insurance, property taxes, homeowners insurance, heating, electric, garbage, water, etc. There are many bills that go into a house outside of just the mortgage.
Also, I know they are family, but keep in mind that if they don't help you out with the payments, they don't loose anything. You are on the mortgage, you're the one whose credit will be shot if you can't make the payments by yourself, which is exactly what a mortgage lender will be reviewing if you are only one applying.