People are free to choose what they want but you mainly keep only the "main" surname from each parent.
I know in England there was a tendency of people keeping both names of powerful families[1][2], then as double-barreled surnames. Which then sometimes went a bit nuts a few generations later if they married into other double-barreled families [3].
I think it was when I visited Stowe School, the seat of the Dukes of Buckingham and looked at the family tree, that I even saw some surnames repeated if they married into other families which shared one of their multi-barreled surnames...
I don't know about the OP, but in Quebec this is fairly common. Usually you have 2 surnames until you turn 18 and then you choose one of them. I really like the idea of this, personally.
I know in England there was a tendency of people keeping both names of powerful families[1][2], then as double-barreled surnames. Which then sometimes went a bit nuts a few generations later if they married into other double-barreled families [3].
I think it was when I visited Stowe School, the seat of the Dukes of Buckingham and looked at the family tree, that I even saw some surnames repeated if they married into other families which shared one of their multi-barreled surnames...
[1] https://www.theguardian.com/lifeandstyle/2017/nov/02/keeping...
[2] https://www.telegraph.co.uk/family/parenting/are-we-heading-...
[3] https://en.wikipedia.org/wiki/Richard_Temple-Nugent-Brydges-...