What about two people or ten fingers on a piano? it's definitely possible and saying it's not implemented because likely not useful is a limiting factor.
In a whack a mole game with 2 players, for example as discussed here
if you have only one group for all the buttons and if you favor user 1 versus user 2 by checking him first, you are twisting the odds of winning.
(As I said, you could solve that with two buttons groups)
Anyway, I'm not trying to convince you. It's OK if we disagree.
My design would be a Button class and then using a container / array to group the buttons. If I need to abstract the group because the group has also some OO meaning, then I would consider a class for the group.