It all depends on the hotel in question. I do believe per the strict T&Cs, only you and one other person in the room are guaranteed access. But in most situations, everyone in the room tend to be given access to the lounge.

If you know the specific hotel you will be staying at, you could search this forum to see if it has an existing thread. There may be info already in that thread or if not, you could ask if anyone has stayed there with 3 or more in a room what the lounge access experience was.