The man should have been more firm in these matters from the getgo. The fact that he had to go to reddit for advice tells me this. Sure seeking counsel is wise but it also reflects the current lack of authority and 'guts' this man has over his spouse. A child's name is a serious matter, this sort of behaviour from the women and co is simply unacceptable.
Thank you for the elaboration. I mostly agree, but these days if a man tries to be "too firm" he is automatically labeled an abuser and emasculated, at least in a secular relationship, which is what it sounds like this is. Granted, that's not always the case, and naturally if the man is firm and the woman is actually behaving like a woman and not a child then the firmness works.
Even if he was more firm, these days of, "muh feminalism, muh rights, muh oppression, muh body muh baby" etc. she probably still would have went behind his back if she was willing to do so when they already agreed not to use the name in a compromise and likely he would have been blackballed for raising a justified fuss about it. I completely agree going to reddit for advice was pretty low and yes names are a very serious matter.