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...
https://www.google.com/#q=why+quaran...w+ball+pythons < some good reading. The first hit is a link to a thread right here on bp.net about qt'ing...