Alright, so hopefully I can make this sound clear.
Currently, my FH has his biological's father's surname. He wasn't in my FH's life very much, but his step-dad (who he calls dad) is. My FH wants to change his surname to his step-father's last name, since he was more of a father to him and he didn't officially get adopted when step-dad and mom got married. We'll both be changing our last names together to the new one when we get married. Right now is legal name is Wilson, but we will both be going to Porter.
On save-the-dates, invitations, etc, should we put on there the our new last name? I can see gifts being written out to "Mr. & Mrs. Wilson", which would not be correct. I'm not sure how to address this. Or should we just leave it all to be announced at the ceremony, where we'll be announced as Mr. and Mrs. Porter. He hasn't told it to everyone yet (his parents, my parents know, I think he told an aunt on his bio-dad's side, who wasn't too thrilled about it, but she's accepting it. His bio-dad does not know as of yet, that I'm aware of, not even entirely sure if he's invited to the wedding...but that's another conversation entirely)