Hi Tia,
I have signed up for NCS Live it with my friends too, to ensure you are all in the same "activity group" you should use the live chat on the website and tell the agent: who you want to be with and the date you have all chosen. In terms of rooms, I think they will be predetermined before we arrive, but I doubt they will really care if you swap rooms with some. I don't think fitness level is much of a problem, all activities are optional and not as strenuous as something like D of E. I would presume you need an average level of fitness.
Hope helps.