10 gallons is usually taken as the minimum for one axolotl - 55 should be fine for juvies and probably ok for adults, but always better to have more room than too little. For one, it makes keeping temperature and conditions good much much easier!
However - It's also about footprint. Axolotls might mooch about the tank a lot when they're little, but as adults they are more prone to staying on the floor. Your tank might be fine volume-wise, (which would keep the conditions fairly well) but if they are constantly on top of one another you're more likely to notice nipping.
As far as floating goes, axolotls (especially little ones) have a tendency to put themselves in ridiculous places and shapes and directions. If there are no other signs of distress (are they trying to get to the bottom but can't?), they are eating, pooping, and visually look ok, its most likely just them having a nice float.
22c is a little high. Water holds more oxygen when it is cold, so your axolotls might be floating near the top to be closer to the surface? Mine often do in summer.