I get this, it's happened to me, friends we holidayed with for years, suddenly invited themselves on our other close friends holiday, and were very dismissive whether we wanted to join in or not. My DH was livid, & the other friends felt terribly awkward, and called us to discuss it. They were also invited to other things, and we were an afterthought, as in you probably won't want to do this , and we've already asked the others but here is the date.
Personally, I feel this is not the way you treat "good friends" free country or not.
But, there were repercussions from that holiday, not everyone gets on in those situations. My advice, let them get on with it and pull back from them both.
Not everyone's view on here, but proves we are all different.