Your parents as Catholics probably should not receive Communion in a Protestant Church.
Well, I'm glad they did... once they understood what it meant! OTOH, my mom did not appreciate her "little girl" not receiving communion in the Catholic church, based on the fact that I had been baptized and brought up Catholic. But I did not believe in transubstantiation and I was no longer a member of the Catholic church, so knowing what they believed, I did not go up for communion. They respected our beliefs and I respected theirs, what's wrong with that?