Sorry for long title but I'm after some rather specific people 
Are your DC known as First Name Extra Middle Name Surname
Or are they just known as First Name DP/Hs Surname
I really really want any future DC to be known by both my surname and DPs.
DP doesn't want them to have a double-barrelled surname.
I wondered if giving them my maiden name as an extra middle name could be a compromise but would they actually be known by both names or would it just be DPs surname that they would be known by?