Ok, so a few suggestions for general roles on the ship are below but I will say in the event that the ship is attacked/attacking you wouldn’t be expected to stick to your ‘job’ slavishly.
First Mate (or Ship's Master): The second in command, in charge when the captain is unavailable or elsewhere.
Boatswain (or "Bosun"): The sergeant of the crew, makes sure the work gets done. Being a boatswain usually involves a lot of shouting.
Gunner: Crew one of the ship's main guns. Load, aim and fire a cannon. The ship needs many gunners.
Whaleboat Crew: Pull one of the whaleboat's oars. Be unafraid to stab a harpoon into a sea creature many, many times larger than you are while standing in a rowboat.
Able Sailor: General purpose sailor, doing all the things necessary to operate the ship. Also participate in the mechanics of whaling, including standing ready to crank a winch (to pull a harpooned creature up out of the water), shoot a leviathan with the swivel gun, throw a harpoon, or anything else you are ordered to do during a hunt.
Rigger: Climb into the sails, make sure they stay trimmed, and keep the ship moving. Sometimes serve as a sharpshooter to use your high vantage point to snipe at enemy crew. If you do not like heights, this is not the job for you.
Lookout: Whether watching from the raised bridge deck on Diamant's stern, or from the crow's nest high in the rigging, the ship's lookouts keep careful watch on the horizon. Must have sharp eyes and the ability to stay awake.
Carpenter: In combat (or a hunt of something really, really big), stand ready to fix holes in the ship, shore up a damaged mast or spar, or anything else aimed at keeping the Diamant afloat when something is doing its best to sink the ship.
Surgeon: If you have medical skill, the crew always feels better knowing someone is there to stitch wounds and splint broken bones.
So general roles I’ve pegged for you guys so far would be as follows:
Christian - Lookout
Andrezi - Able Seaman (Carpenter wouldn’t be too much of a stretch based on his background though either)
Dr Bastien - Ships Surgeon
Llorenco - First Mate / Boatswain (based on their past naval experience)
