I think your child's biological father may have something to say about this. He does have rights and will need to be consulted, no matter who is seeking to bring the child to the UK.
My stepchildrens' father had the good manners to pass way before he needed to be involved, and his name was never put on their BIRTH CERTIFICATES anyway.
They have to say 'father unknown'.
THAT is the crucial factor in your case.
I think you need to prepare yourselves for a struggle and a lot of form filling, sorry to say.
