Hiya strat and welcome to Aquariumadvice!
There are a number of causes of swim bladder issues:
Infection, as you are aware of. Could be viral or bacterial. Its near impossible to tell the difference.
Dietary. Flake foods, for example, cause bloating which can throw off a fish's ability to maintain neutral bouyance.
Constipation. Yep, fish get constipated. Also diet related; over feeding can cause blockages which will affect the swim bladder.
Anatomy. Some fish are simply prone to swim bladder issues, like some of those funky goldfish.
Toxins, especially hydrogen sulfide which happens in anaerobic conditions, such as in tank decor that doesn't have water moving thru it.
My guess is your guys have either a viral or bacterial infection, especially since whatever is going on appears to be infectious. But before we do anything, check ammonia ph
nitrite and nitrates (don't forget the last 2; grab them from a Petsmart or something thats open late so you can be sure those are ok tonite). That may also indicate if there is a water husbandry issue as well.
I would do a decent size water change (I do one after any fish gets ill or dies), and remove any ill seeming fish ASAP
to a QT
so they don't keep infecting the tank (whenever a fish starts looking unhealthy anyway).