It's certainly an awkward, and potentially an unpleasant situation.
Personally, I'm pretty rubbish at this sort of thing, I prefer to just play for bands, rather than joining them. I would absolutely hate to be sax number 1, and find that I'm out of the band. He obviously seems to enjoy it, even though he has other things on.
It seems to me at least, that the band isn't really a 'serious' thing, though I may be wrong. So could it not be more of a collective of musicians rather than a band ? So whoever can make it to a rehearsal or gig does, and if they can't, then they can't. The 2 saxes can work things out between them, as to who plays what, and when.
It is Christmas too .