" I sealed a few areas on the exterior that might have been the source of the leak but how do I know if it’s been fixed? "

You verify before you put up new drywall and finish the interior. What were the leaks you repaired and how did you repair them?

There’s a chimney on the opposite side of the wall that didn’t have good flashing/sealant where it met the siding. I filled the gaps with silicone to seal it up but guess I don’t have any way of confirming that it was the source of the leak to begin with without opening up the wall and testing it?

I would cut out the area of bubbled drywall since it’s so east to replace. Spray the suspect area around the chimney with water from a hose for a while and watch for leaks inside.

Who did the installation? Get them back.

"this exterior wall was completely reframed"

"didn’t have good flashing/sealant where it met the siding"

Without pics and more info, an exterior wall that needs completely reframed probably means there was a large expanse of fatal rot. A chimney enclosure meeting a siding wall probably means a vertical joint, which would have less chance of contributing a lot of water. Poor flashing on the roof or a compromised mortar cap would be a more telling scenario.

It's always the im[proper flashing.