I do hope they haven't infected the rest of your flock.
Ditto. The idea with quarantine is no contact with your flock for 6 weeks, with these I would have done six weeks of healthy. I hope the rooster can't get back in with your existing flock? Or is he it? Or whatever these have so will they and you could loose the lot.
I think I would be worming them as well. If the mites weren't taken care of there is a goodf chance they will have internal parasites too. The ivermectin will kill some but not all types of worms so do a search to find the wormer will take care of the rest. (Sorry can't remember the name)
Good luck!