All this calls to mind the reasons I didn;t have a wedding - family members who disliked each other,business friends of my father who had to be asked, all that. I just opted out and had no-one except my parents, god-mother and my mother-in-law to be. Much easier. Alma Jr should have done the same.
But then of course the movie couldn't have had that scene, and that's the point of the whole thing - it's not really meant to be logical in the terms in which we're analyzing it. that said, Alma Jr's cataloguing of who's doing what make sit all sound a fait accompli and leaves Ennis with little option but to say yes to everything or no and look bad.