Barakus Question (spoiler)

So S&W question. My players are currently in Barakus on 1-24 F with the fire ball door.

 

They were able to do 1 knock spell and barely survived and still have 2 more locks to go.

 

Is there a way for them to unlock the two other doors without taking 2 more fireballs to face using the knock spells and or finding the keys?

There is only a single fireball that triggers whether a thief attempts to pick the lock or the first knock spell is cast. Notice it states the door is trapped not each individual lock. It doesn't say but I would probably have the fireball reset after a certain time (about 1 hour/6 turns) if the party walks away.

Of course, you can still hint that the status of the trap is unknown until the second knock is cast.