I just finished a similar sort of ordeal, except it was an ABBA tribute thing.
The singers made up stuff and came in whenever they felt like it. No amount of rehearsing the openings and endings could get them to do it the same every time.
The guitar player is an amazing player - if you are doing country, or blues or rock, but if he hasn't been doing it for 30 years, it isn't going to happen. I ended up taking a number of guitar leads on my bass (24 frets and an Ampeg SVP BSP made it possible). Jaco may not have needed 5 strings or 24 frets, but I sure did, and I'm no where near that sort of talent. I only left one fret unused, which never happens in written bass parts. Thank god I wasn't on a Fender - this gig convinced me to sell them off as they were too limiting.
The sax player was as white as they get, which you'd think would be good for an ABBA gig. But timid late entrances and a thin tone don't work anywhere for anything I have ever been involved in.
Drummer was a bit under prepared, but a good player with fast ears and actually did a very good job.
I don't know that I'll ever be involved with these charts again, which is a pity because they are actually well crafted, but non reading "musicians" can F up anything.
Education: the path from cocky ignorance to miserable uncertainty.
The chains of habit are too light to be felt until they’re too heavy to broken.