Most people nowadays wouldn't nn a
William Bill, so it's probably
Will and
Ben when they are at school, though they do run a risk of being called
Bill and
Ben I don't think too many will take notice. I certainly didn't think of it until you pointed it out.
Peter and
Benjamin are too classic names, and though it might of been done on purpose, I doubt it. Unless they have a sister
Jemima :)