Mad scientist fits up to 8. Pocono moonshiner fits up to 6. It is definitely very difficult for only 2-3 individuals. The curse of the pharaoh will fit up to 8 and is nearing completion.
I think it says 8 people maximum on the website. Having done 2 of their rooms, I wouldn't recommend any more than 4 or 5.
2-8 would probably work. 2 might be hard because the clues work better with a lot of ideas and 8 might be a bit crowded.
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