When we had 24 of us at the Fall Texas Hang last November, we were at Springfield area and used 5 sites. We had plenty of room for more to hang as well.
Some considerations about Texas State Parks to be aware of as planning occurs:
1. There is a per person entry fee in addition to the site fee.
2. No firewood gathering is allowed. That includes the primitive area. (Makes car camping with a trialer of firewood like we did more appealing.)
3. Reservations can be made in advace that guarantees a site. Specific sites are first come first serve but if someone arrives early on Friday or anytime on Thursday, you get pick of the litter.
4. At Fairfield, they are very Hammock friendly and allowed us to move beyond the edge of the sites into the wooded are further if we needed for sufficient trees.
5. In the car camp areas there is a limit of 2 vehicles per site, (part of our reason for using 5 sites when we could have crammed into 3), but there is a big parking lot at the trail head with no vehicle limit for that primitive area.