This probably won't surprise those of you who know me by now, but I really think some of these would be quite amusing at the very least:
Treize Khushrenada and
Reinhard Von Lohengramm discussing politics alongside
Yang Wenli and my grandfather... I'm sure it would stay controlled at all times since none of them seem the type to get too heated, but just the very thought of them all sitting at the same table all putting on their proper manners and formalities while discussing various issues would be quite amusing.

Just imagine how insanely awesome this would be
On the younger end of the table(s) we'd have
Akiha Tohno berating my younger brother for his poor table manners and not using his silverware properly,
Shiki Ryougi would be stabbing her brussel sprouts with her knife in an attempt to "kill" the bad taste, and
Kohaku would be helping my grandmother and one aunt in the kitchen while
Hisui assisted my other aunt and I with cleaning up the aftermath.
Hitagi Senjogahara would probably be sitting near my older sister destroying her in a battle of wits, while one of my cousins around my age (who is sometimes referred to as the "one man boy band") would probably make several attempts at courting her, but she'd probably ruthlessly destroy his ambitions even while they both keep smiling.
Meanwhile,
Boota would be hanging with my Chow/Sheltie, Peanut, cowering under the table from my Uncle's cute-but-territorial Husky/Greyhound, Molly.
Of coure,
Yotsuba Koiwai would be plenty welcome with some of my cousins at the kids' table, and I'm sure she'd get along great with some of my aunt's friend's kids.
Seriously though, that'd be an awesome Thanksgiving...