For a big tent Buck has a nice setup for sale. I have a TI 6.5 and would think the 7.5 with three would be fine.
https://www.24hourcampfire.com/ubbth..._Titanium_Goat_Vertex_7_5_Ti#Post9275098

The Backcountry Shelter would be an excellent choice, being modular you could join them for your big group and then have two smaller tents for the rest of the season. I'd see what they could do for you.

http://store.seekoutside.com/backcountry-shelter/