As long as you play your character well, and the team works together well I don't see any need to worry about what class/role remains to be filled. But since I have no idea how well these 3 and you will work together, I'll point out that from the character sheets I've seen, nobody has prepared any healing whatsoever, and they are also all lacking the social skills one might hope to have when helping out in a criminal investigation. Actually, this particular module seems custom made for inquisitors, and the current party is anything but inquisitors. But play whatever you want :D
