We were 11 people staying in the apartment, and it worked out great. Since it's only one bathroom, the bathroom line in the mornings got quite long, but it worked out completely fine. It was a nice apartment that had walking distance to most things. You should buy all groceries before, because it's a 20 min walk to the nearest one with a decent size. Just remember when you check in to check if it's enough sheets, blankets, pillows and towels. But if it's not, there is no problem, they will bring you extras, and they do it pretty fast as well.
We really enjoyed our stay and if we go back to Montreal we will definitive consider staying here again. The host was really nice and helped us out with all of our questions.