If you have a scenario like that, then you don't really need the communication app. But it sounds like you don't, because you mentioned players not making it every games.
Why not set out your "regular group" of 9, then a second group of alternates that only can come if a regular is not available. You could still use a communication app, just make it clear to everyone who the regulars are, and who the alternates are.
Do people get butt hurt by that? If I was in that crew, I'd want my "alternate" status hidden from myself and others, LOL. It's the reality but it wouldn't encourage me to make an effort to show up.
But yeah, good idea about having different groups like that. I'm at the stage of still looking to pull together the "regular group" of 9 first.