Only one camera will record at a time. I have five cameras set up. If one is recording at one end of the house none of the others will record.
Well, not my experience with XT2 cameras.
I have two XT2 cameras facing my entrance and garage and both can record simultaneously when someone enter its zone.
As I recall, this was an issue/limit with the original XT cameras. Dunno if that ever got updated or not.