I've had some trouble coming up with side characters (aka, the members of the commune), but I finally figured out a process.
Piles of people!
I'm totally normal, right? Right.
I think the reason this has really helped me is that I'm a visual person. I've had "concept photos" of my main characters since the beginning. Looking at a person's face helps me envision an entire life for them. Helps me figure out who they are. A face is the starting point. Give me that and I can create an entire world.
I know a lot of people don't function like this. They're less visual or perhaps just less OCD. That's great.
This is the kind of background work that often isn't obvious in a finished novel, but even if you don't memorize the charts, even if you don't keep track of who is related to whom and how they got there, I hope I can give you a depth. The impression of a real community - of real people who live and love and work together through all the trials that I will undoubtedly put them through.