A few bands ago, one of the guitarists turned out to be quite deaf, a bit doddery and not very well dressed. I thought I could put up with it as the singer and the drummer were very good and the other guitarist was reasonable. Then the singer was asked to leave as there were issues with his attitude.
The whole thing eventually was solved when the drummer moved house out of the area and I made my excuses as we now had no singer and no drummer, and I moved on (well, I was already playing with a couple of other bands anyway so wasn't too big a step).
So you do have the option of leaving. I'm not a fan of sacking musicians, it kind of marks you as being a bit arrogant and above the others if it's just a hobby band.
Have any audience members or bookers said anything? Are they playing badly? Missing sections, playing wrong notes, slowing down as the night progresses, ordering hot chocolate at the bar...