Bloody hell, Wilhelmina?! 🙈
So the child gets his surname, and his family tradition also chooses the child’s middle name, and apparently your feminised surname isn’t an option, and now he’s managed to also make it impossible to use your favourite name.
That’s quite bossy of him. I would not be happy.
I would push back a bit on the middle name but if it means that much to him I would probably as my final offer give the child two middle names (and just never use them except on official paperwork). Plenty of people have four names.
so eg Willow Laura Wilhelmina Jones.
If he isn’t happy with that either then he needs to go look up compromise in a dictionary.
If you actively hate the name Wilhelmina then that’s a problem. You shouldn’t have to gove yiur daughter a name you hate. If you really hate it, just say so. Say you respect him and his family traditions but you cannot give your daughter a name you actively hate.
Surely his mother had a nickname? I do not believe everyone said her full first name every single time they spoke to her.