I agree with Sue25. I have my bantams in with 'biggers' as I call them, Welsummer and Buff O hens. No problem. The Wellys are a little 'pecking order' obsessed but all in all they get along very well. In fact, the Welsummer hens beat up the OEGB/BBR cockerels that I have regularly. Not too easy on the OEGB cockerel's egos but funny as all get out to watch.
You should try to catch them and rehome them. They will probably get killed by something if you don't.