quite like the idea of changing my name to Dp surname-my surname, then giving the baby Dp's surname only. Then as mentioned by PP I'd still be linked to all of the children.
I think (as I suggested), this is a good solution all round.
Regarding your DC5 feeling different, they will grow to know that the rest of their siblings have another dad.
If they are visiting dad, DC5 won't be going, so I don't think that's a good enough reason to give the baby your Exes surname.
Honestly has if I was a man, I'd feel terribly insulted about it. It would feel like a slap in the face.
Sometimes it's so important to place yourself in the other person's shoes.
Imagine if it was your son or your brother who was the DP in this scenario. It's like being sidelined (from his POV) that his child would have the surname originating from the abusive Ex H.
There's no way I say it that it sounds right.
Ferris, by that thinking, it's also saying that her DPs name (father of the child), isn't good enough for the DC.
Good enough to be a dad and but not for the child to have his surname.
OP, what's the age gap between DC4 and DC5 going to be?
Will they even be in school together?