My wife works here. You need 2-8 players, but the recommend more than 2. Some of the games are a bit more challenging, bit if they aren't busy, they will let you play with 2. :)
They have different rooms if there is a big group. We had 14 people and we were divided in two groups. They have two same rooms if you want.
The rooms are design for 5 to 8 people. They will ask if you are comfortable with grouping up with other people/groups in order to fill capacity but I haven't heard of them turning anyone away for not having anyone to go with.
I think it depends on how busy they are when you go in. When I was there, they allowed 2 people to do it without adding any others.
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