I don’t think they ever said what happens, but my guess would be the holodeck splits the simulation space in two (or more) pieces. There must be a limit on how much space each separate person needs for the simulation to remain realistic but it seems like a fairly large number of people can split off. On Star Trek Voyager they simulated a town using two holodecks and would have quite a few people in it.
People who want to fuck. That seems to be mostly what Quark’s customers use his holosuites for. I recall someone being shocked that Sisko let his son use them, but Quark explained that he just plays baseball in it.
