Far too matchy for my tastes, it makes it a bit tacky and cheesy. I don't like matchy names/nicknames for twins - they need some kind of identity besides the fact that they're twins and super similar names just doesn't help!
Wilhelmina (this spelling) is nice but
Roberta is a bit clunky for me - I don't like
Robert either.
Bobbi and
Billie aren't my style as I don't like boys names on girls, and I consider those boys names.