He had been living with his step dad (also legal father) as much as he has been his mother.
This isn't a usual go situation and the child's main residency is with the gp
Op it appears that, from one point if view, that the father of the baby fucked off to Germany, your dh offered to take the baby on and that was good enough at the time. You don't like you MIL and call her a problem in the relationship, but let her have primary care of your child. In the year the bio father has been back you couldn't deal with childcare between 3 of you?
You chose this path. You chose to put him on the birth certificate. You chose to let him be the father and her, the primary carer.
It's not a childcare situation like nursery. He lives at her house lost of the time. She isn't a qualified professional and you are a customer. What you pay her is the equivalent to CMS.
Allowing your husband to be the child's father legally, but only as long as he is with you is awful . I bet you would be loaning if dh said he wanted no contact with the boy, because he isn't his real dad. Wouldn't you be asking if the child meant anything to him.
You can go e your child a father then just remove him. Well you can. But your shouldn't.
The child needs to start coming first