“Which of these allow Catholics to join?”
It would appear that all do. Look at the statement of principles/faith for all of them. The only one that gave me pause was medi-share as they have a sola scriptura perspective. I don’t pretend to be a theologian, but I saw nothing in the others that would prevent participation as a Catholic.
The reason I asked is that a FReeper in a previous thread said he found only one that did accept Catholics, but he didn’t say which.