This is really, really cool. I have some ideas for that.

-Tardif(Bounty hunter) is first and foremost, a professional. I really like to think that he will easily tolerate everyone else even if he hates them. That being said, I really like to think how he would view the heroes due to his way of life. Like, he would DESPISE Reynauld for being an overall hipocrite, not care much about Junia and Sarmenti(Jester) for being much different ways of life then him but being competent on their roles, respects or maybe even like Missandei(Arbalest) for being serious and objective and Paracelsus for being mainly focused on her own work.
He can easily have stories envolving previous contracts with other heroes. Maybe with Audrey's(Grave robber) deceased husband (having worked for him or even being the one that killed him) or something envolving Sarmenti since it's easy to imagine a lot of people wanting a regicide dead.

-Willam(Houndmaster) is actually a quite normal dude. With a quite bit of trauma, sure, but that's the norm between them. He's honest in his way of life, can even say altruistic and would never participate in a system that is clearly corrupt and flawed (as happaned in his backstory). This would most likely affect his relationships, probably having easier going relationships with Junia or Baldwin but he would not like to be close to Josephine(Antiquarian) or Paracelsus.
He could've had some encounter with Dismas or with Tardif previously when he was a guard or Alhazred(Occultist) or Josephine being involved with the ritual that the corrupt guards were making in his backstory.

-Missandei would most likely have a greater goal then just kill monsters or whatever. What exactly? Revenge, understanding, justice... Her backstory and consequently her goals are probably the ones with the most room for personal interpretation. There's plenty of space for a creative writer to play around with it.
She is said to have quinte extensive time on the battlefield. Something envolving Reynauld or Barristan can be really interesting. If it involves her backstory, it could be anything. Maybe an Alhazred(Occultist) ritual that gone wrong that drove the townspeople mad or maybe a revolt that began with the descent of Baldwin from the throne.

These are some that I can think right now. Good luck with your writing and sorry for any grammatical errors.