I am Catholic. Was a groomsmen at a Catholic wedding (full mass! eff yeah!) Only 2 of the 4 of us sat, stood, kneeled. I don't know, I'm not judgey at all about any of these things. I don't know many Catholics that are.
I just found it to be a dick move on their part.
Also, I don't think Catholic rules apply to non catholics about communion. If it isn't part of your faith, then it's not. Take communion, don't. Who cares.