I have an "S" corp, my business partner has an "S" corp. We are buying another "S" corp (50/50) is that allowed? Same situation except we are buying a LLC. Is that allowed?

Are both of you, individually buying it? Sure, that's allowed. But if your partnership is buying it, no: I don't believe anything but a natural person can own a corporation if a subchapter "S" election is desired.

And yes, I see no reason why the both of you individually, or the partnership, cannot own the LLC. But you should check your state's LLC statute to be sure.