3 "Q's" + POTUS = 4 devices
Relay chat. Yes. Q also uses SATCOM so the devices have to connect properly before they can send the posts.
After 9 months, what it seems like is that they don't post as Q unless all of them are present. If anyone of them are out of the country (Pompeo in NK, Dunford overseas, etc) they don't post as Q but they may sometimes post as anon.