At the beginning they're all quite set on their own agendas, making them companions of convenience only. Not much trust there. Later on as cracks begin showing in their missions and more shared experiences, trust builds.
Lae'zel suffers from minion delusion, her society built on a lie that the artefact could expose, and her cure is probably just decapitation, hidden from trainees so they dutifully report themselves. As this all reveals itself, she'll probably have to concede and switch to relying on Tav's efforts. She brushed off Kith'rak's words as disloyal, so she'll probably need to see she's 100% a tool before she becomes reliable.
Shadowheart is Faerun's worst secret agent. Maybe she was elite before tadpolling, but I don't think so. Her value is probably whatever suppressed memory than any secret agent skill. With a bit of dogged persuasion she spills basically everything she knows, which is little more than minion need-to-know stuff. Even this recover memories is suspect, I'm not sure which spell below level 9 Miracle or Wish could undo it - and why would such a powerful cleric restore some minion?
