Now, you could theoretically have 4 congregations in one hall pretty easily, and maybe 5 if one was willing to meet on Saturday.
Fencing ...
Not sure where you live but here in South Florida 4 and 5 congregations meeting in the same hall is the norm, as are tri-plexes (3 KH's built together). I know a couple of the tri-plexes that have a total of 15 congregations each. I can't think of a KH here that doesn't have at least 4 congregations in it. We currently have 4 congregations in our KH, Mon-Thr nights with the 2 WT studies on Sat and 2 on Sunday (people here don't like late Sunday meetings ... Saturday is preferable).
Rub a Dub