Sure will try and help you if i can. Let me know the names of the girls and their birthdates......most, but not all, moms leave the first and middle names the same and just change the last name. My husband adopted my two children from my first marriage, but we never kept it a secret from the bio family, but they just thought we'd given them a transfusion instead of just a name change. The girls probably know all about their bio dad, maybe a little color=ed from the mom;s point of view, but most step father adoptees know about their daddies. It is no secret, the families know.
keep in touch and i will try and help you.
thanks for writing
Normaj