2007 Chevy Malibu Fuel Level

The problem I have is that 1. my fuel gauge does not read how much fuel is in the tank and 2. the information center does not tell me how many miles i have left in the tank and 3. my check engine light is on. I had my step-father who is a certified mechanic but not for GM check the code and it said something about the fuel pressure. I believe that the fuel pressure sensor is out. He told me to fix the fuel gauge I need to replace the fuel pump which is $300-$500 depending. Well I believe that all I have to replace is the fuel level sensor and the fuel pressure sensor. Is my thinking correct or do I have to replace the fuel pump? Thanks for any help you can give me.