One betta died; other two acting lethargic

[hmckin20]

So I stumbled across Goliath and Soldier acting lethargic and chilling around the bottom of the tank this morning.
After looking for Flair I realized he was dead. I'm not certain what killed him- ammonia levels probably. I'm still cycling the tank.

I put the other two in separate bins with clean water and some AQ salts, and they seemed to have a suspicious icky film- or something- on their bodies. I put a pinch of fungus meds in there too just in case.

Do you guys think there's anything else I can do? Do you think they'll survive?