I feel like there's gotta be a few people who have their superstar musicians actually in a band of other playable or townie Sims at peak Creativity skill, just because it's fun seeing them actually perform (as opposed to getting in a carpool and disappearing all day like happens if it's only the career track), but how do you set your game up such that 'the band' is actually all playable/controllable to allow for this kind of thing? Do you have them all live together so they're all playable members of the same household? Do you temporarily make the other band members selectable when it's time for a performance? Etc., etc.... how do you handled actually getting the whole band on stage at once?

Usually I have the band live together, but sooner or later there tends to be a reason for them to live separately. In which case the band can break up, or you can try putting them all into a (Band Name) social group and call periodic outings to suitable venues, and have the active sim use the "join" interaction to get them all playing together. If somebody else slides onto an instrument before someone can join, well, there's a guest artist. If somebody gets on the "wrong" instrument, they're mixing it up, keeping it fresh. And if everybody quits after only a couple of bars, well, you don't have to admit it in the story album. It's really annoying, though.

I use the group thing too (manage groups on the phone); make sims selectable if needed and have added some extra instruments at every venue.

However, sometimes, whatever is happening on (and off) stage is far too entertaining to interrupt!

(But I don't care so much, go with the flow, except when it is my elderly band, then I make sure all of them are on stage).

My bands live apart but if I want them to play a gig here is what happens:

If I'm not playing a band-member's lot

So sometimes I have a sim out at a club or about town, at the local music dive bar, and if I want 'my band' then I -

1. Import them in with Sim Blender or Sim Manipulator
2. Make them selectable with Sim Manipulator
3. Direct them to go perform for tips to their respective instruments

If I am playing a band-member's lot
1. Have them walk to the venue
2. Import in their band members like step 1 above
3. Make them selectable like step 2 above
4. Direct them to go join my playable sim on their respective instruments

The reason I don't do groups is because the other bandmates could be at work and not available, teleporting them in makes them available no matter what, and the reason I don't use 'ask to join' on the other bandmates is because they could wind up at different instruments than what they 'should' play.

For extra hassle but immersion, I also sometimes either 'pack' up my sim's instruments in their inventory and pull them out at the venue or grab instruments from the catalog to place directly on the venue with the buy/build/inventory access on community lot mod