We stress quarantine because that is important. When most people answer questions on here they do it for everyone that may read it in the future, not just the asker. That is why I stated that right now, quarantine and vet visits need to be worried about. At this point, you're right though, quarantine is useless. Vet visits need to be made. And rechecked in 30 days (at least the fecals) for EVERY glider, as they've already been exposed to one another.
Everything that I have read has said that there is no need to really worry unless the gliders are balling up to the point where you cannot separate them. Hissing at each other is fine, and normal. When I first attempted to re-intro my two after a separation period for an injury, they would "wrestle" but I was told to keep doing what I was doing so long as they weren't balling up.. Just watch closely.
That said, any further introductions should wait until the gliders are all relatively the same size, as otherwise the smaller glider could get injured. Any further introductions should also take place in a neutral territory.