I do realise that there are legal ways of registering but there are numerous example of little white lies! on certificates.
I think we all have examples.
I think if all the family have accepted that they all have same father and he is happy to be called dad its the families choice.
My grandmother didn't have that choice born in the workhouse mother was named but she didn't stay around took me a few years to find her mothers mum only to find she had been born in workhouse!!