It's 15 bantams. Wouldn't they get scared and hurt each other in the crate? I mean weeks is a long time. But the past owner was an impulsive buyer so I don't think that they will have good health...Hmmmmmm, thats a hard one. Do you have a cage or something?
You can put them right in with the flock, but it's taking a risk.
Maybe put them in a small cage inside your coop if that's possible?