If you haven't seen mites for two weeks, I'd think you are good to go in that regard. However, 4 weeks isn't a long enough quarantine period for a healthy mite-free snake, much less, one you received with mites. I'd quarantine the new additions for at least 3 months...preferably 6 months...the longer the better...
X2
Mites are a nuisance, the real problem is the disease and parasites they might transmit.
And, QT is not just for mites and mite related infection/infestations.