These kids are not yours, they are his…
And it will stay that way forever.
What does that mean?
That their biological mother stays their mother.
You have less power than the biological parents in the equation.
And it’s essential you don’t try to fight that because it’s a lost cause.
You have no legal power and if sensitive decisions need to be taken concerning these kids, you might be consulted but you will notice that you are NOT the one making the decisions here.