Mmm... I was actually thinking along the same lines as L.Radiance...
I don't know the background, so like she said, perhaps this is off-kilter. You don't think that you are being invited to activities out of friendliness? You don't think that your partners' partners are perhaps trying to be kind?
Those are just questions.
But the crux of the matter... no, I don't think that one person's relationship is down to the dictation of another person.
The only difficulty is that in poly, one relationship does tend to effect another, even in some small way. That doesn't mean that metamours have a right to decide what goes on *within* the relationship.... but of course, they do have a right to freedom of speech and voicing their needs and wants.
It's strange... usually, people post because their metamour is trying to take time *away* from their relationship... ~grins~
Me: (30f) open poly
GF: (40f) My long-term, long-distance partner
Hubby (37m): GF's husband
Garcon (26m): GF's submissive/third partner
“Peace comes from within. Do not seek it without." ~ Buddha