Re: Adding a Last Name to a Child's
You can ask a court pretty much anything you want. The court will rule in what they believe the best interest of the child is. They may allow a hyphenated name but in reality, how does that serve your purpose? They will still have a different last name than you and the sibling.
You do need to get rid of the idea that they have "daddy's" name. If you have the same last name, you really need to keep it that you want them to share your name. Courts don't like back door adoptions where people play the name change game so it appears the children are of different parentage than they really are.
You make an odd statement though. In one sentence you imply the father has not been around at all (they don't remember their father (and he is not their bio father. He is their father) but later you say the father will not consent to the name change. That suggests you have had recent contact with him. Which is it?
I am not an attorney and any advice is not to be construed as legal advice. You might even want to ignore my advice. Actually, there are plenty of real attorneys that you might want to ignore as well.