Members of the Prostetant religion or faith. It's a form of Christiantity.

I imagine you've been able to find this in a dictionary already, but "denomination" is similar to constituted (or something along those lines). You might also say "US dollar-denominated accounts."

actually protestant faith*, once there are the catholics who are also christians, but not protestants.

The subdivision of the christian faith to which one belongs is called their "protestant denomination".