Why would that be controversial? Politicians/heads of state are also people with friends, just like everyone else. As long as they are listed as friends of the couple (not representing their country), I see no problem with that.
Yes, and I’m sure statements will go out from the palace beforehand that they are attending as personal guests of the couple so there will be no confusion. It’d be awfully sad if you can’t invite friends that are dear to you just because which family you belong to and how successful they are.