Large group camping in the backcountry

[McTullis]

We have a possible group of around 14-20 people and 4-5 vehicles coming down to BIBE in mid October. I know that the Terlingua Abajo sites are three that are relatively close together and could meet our backcountry needs, but in the event we can't camp there when we arrive, are there any other suggested backcountry places that could keep our group within short distance to hang out together? Has anyone camped at Grapevine Hills 1 that holds like 20 people? I can't seem to picture it in my head.