Mortgage Help for "thin file" little credit?

I have 19 years and my girlfriend me getting married and want to get a house they both work full time that i make about 15000 and 25000 each year is also want your mom to move in moving 12,000 a year to help with the mortgage. My girlfriend has bad credit due to no health insurance so you have medical bills and the city lived in profits in the left anterior direction of six years in one place so that she has thousands owed to public services and mom is in the same boat. Now I'm a full time student in college I work hard like my girlfriend and I want to be able to get a house. On paper I do very little, but I have only good credit with my car payment that has been paid on time for 10 month life of the loan is 2 years (total $ 2500) although I am saving and will have paid off by February and although the only thing on my credit is my student loans (totaling $ 8250) which I am on good terms with, I know all this because I checked my credit report, but not my credit score because it costs money and I don 't have a credit card but I also requested a Discover card and has rejected my credit controls were only two times when I was looking for a car and my bank twice trying to get credit in the protection project and my car loan one has a co-signer. I'm not living with my father, but the rent is not my name all invoices are fine, but only from July this year. The market for the house I live we could get a good home for about 50,000 would not be able to make a large down payment but want to take only a ten-year loan and could afford an interest rate of up to 9 %. We have heard we will extend the 8000 first time home buyer tax return until April of the following year, which would be good for the house payment early, but would really like to be in a home by next summer and 8K would good too, but the things I do to try to get this accomplished. Could I get a credit card with an annual fee and balance payment is always a good idea because I thought the cards you have to pay for that are scams or not reported to credit bureaus and how I can get pre-approval and this would be a good idea at this time or would be a waist of my time and make my score worse?