Childs biological father passed away. How to handle this situation

The hospital would not let me put his name on the birth certificate because they said he had to be there to sign it (This was in 2003). Well, he passed away before my son was born so I don't see how that's possible. In 2012, I married my husband. His daughters mother took him for child support and the court won't recognize my son as another child that he is financially responsible for (even though he lives with us). We also have a one year old. They can't pretend my 10 year old son doesn't live with us. It's not fair. My husband is the only one working and he fully supports my son. They're taking him for every penny as if he has no other kids. How do we go about dealing with this?