I'm in a similar situation. I have 5 layers, two moms with 16 chicks, a rooster, 15 meat birds, and 2 ducks in the same space. They all get let out during the day. I try to give the chicks flock raiser and keep the other birds away.
I don't have them on starter because I thought it would be too much trouble to keep them segregated and happy and I didn't want the other birds getting medicated feed. Yes, I know they make unmedicated starter but it is hard to find in my neck of the woods and the chicks running around are building a natural immunity I hope.
Because I have everyone mixed they get the layer ration and whatever they find in the yard. If they didn't roam during the day I would be more concerned.
If all your birds are confined there could be problems with the chicks and the layer ration. Wait, they aren't chicks, they're 3 months old. I don't see a problem even though the feed bag says wait.
May not be the right way or best way, just what I'm doing.