When my Rhysida longipes had babies, I kept the plings together longer than I would have liked, but they seemingly did perfectly fine. So I suppose you could keep them together, but like others said, I wouldn’t try it.
I've got three communal set-ups with S. mutilans. Two and small groups of juveniles, the other is a small group of adults that have been together for quite a while (don't remember exactly how long, but definitely more than a year). Where some people go wrong in their communal set-ups is in overcrowding. "Communal" does not mean that there aren't limits on population density. I give mine plenty of space, deep substrate, more complex environment (leaf litter on the surface, bark, rocks, etc.).