Yes you should absolutely change the water if the levels are that high. You are not going to hurt your fish or the cycle by doing so. IMO
returning your fish is pointless now because you won't get money for them (at least you wouldn't where I'm at) Just keep up with pwc
and monitor the ammonia and nitrites if u can. Feed them sparingly (like a pinch every other day). Really pay close attention to their breathing and watch for ammonia poisoning. If u keep up with the pwc
I think your fish will be fine (but do not add any more to it)
As for the bubbles I have never seen that before. I'm not sure what is causing that. Do you have an airstone ? Maybe there's too much air coming into the tank? I'm really just guessing here.