Usually it's whoever you can fit in your car. The sites are tiny though, so depending on the number of people in your group I suggest taking multiple cars with multiple sites, and driving in together so you're next to each other and can make one huge site. I'd never do more than 2-4 people per site.
We have had up to 5 people at our site with no problem. As long as you pay for camping I think you can take as many as you can fit.
Agree with Chelsea on the # of people. Also note standard camping will give u a smaller site. While premier they give u a bit more room. And free showers.
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