4 names is extremely common here in Europe, not sure what the problem is. I myself have 4, for example. You usually pick 1 or 2 of yours to pass down and 1 or 2 of the mother's so in that sense double naming actually seems like it would make the proccess easier, no?
And let's be honest, when you get married to someone you only pick one singla name to adopt, it's never more than that so this problem is nonexistant.
Regardless, double name or no name are the only two options that make any logical sense, if you ask me... you either take each other's name as a sign of the commitment to each other you're about to make or neither of you does, at the end of the day it's all about making a commitment to someone on equal grounds, only one person taking the other's name is more akin to cattle branding than anything.