I would quick add that duplicates of the same role may not be totally out of line.

What happens if we..."run out" of a mechanic? Also, wouldn't multiple mechanics work faster and have more to interact about?
If nothing else, at least the characters would have the situation they're presented.

Even if its superficial, multiple convicts seeking to be relevant would vie for the opportunity to be relevant...or detrimental, based on their alignment.
There could, arguably, be more than one of a role when you consider context.

How many cannons are on the ship?
Where is damage to a system from a source located, and how many locations of damage?
How many people are hurt from a [i]something[/i]?

People with knowledge of first aid, at least simple mechanics, military experience and piloting would be required. The more the merrier, and the more we have, the less the Committee has to worry about where to put them.

Still, the limit should be (AT MOST) [b]2[/b] of a major role.
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Although, I'm not a GM, so this is all pretty much speculation.
Seek Gm/Co-Gm approval.