surname of bub when parents have different surnames

[AnyDream]

My DDs both have two second names, one of which is my surname, then DH's surname for a surname. Written it looks like this

Harriet Scarlett Gxxxx(my surname) Wxxxx(DH's surname)

so if any time they want to start using my surname in a double-barrelled way (or even by itself), they can, but DH's surname is the surname on their birth certificate. My surname is much longer than DH's and doesn't really hang together as a double-barrelled name too well so I figure this is a simple way around it.