We've had as many as 6 people at a time in camp at my fathers 37 acre site. But we also have thousands of acres nearby that are State or County land. Many of us go there to hunt also.
And we seldom have all members (9) in camp at one time, due to preexisting commitments.
So for 100 acres, as OT mentioned. Its up to you and how safe you feel with however many people you have involved.