Just saw this threada pop up -sorry if my post is a bit off-topic, but I wanted to say that your Protestant guests, while intellectually understanding closed Communion, can be pretty traumatized by it if they're accustomed to open Communion.
It wasn't that I felt unwelcomed - I didn't - but almost bereaved visiting Mass. (I know that sounds like an exaggeration, but it was my experience.) Communion has since college days has been such a point of connection to the Lord for me and I haven't taken it lightly since.
My only visit to a regular Mass a few years ago was so unexpectedly traumatic that I doubt I'll be able to go back to a Catholic or Orthodox Church other than for something like a wedding or funeral. My cousin explained everything to me, said her priest welcomed non-Catholics for a blessing, told me how to cross my arms, and I was good to go ...but as Communion started, I started crying, then sobbing. I barely made it to the restroom before I started actually bawling. I felt bad for my cousin and felt pretty awful myself.
I'm not posting this to argue with closed Communion; I understand why it's practiced and would never take it in a church that practices it. My point is there are some of us Protestants who know deeply that we're part of the Body that is the Bride of Christ, and to be deprived of our Groom is worse than not feeling welcomed.