The first time I cooked Xmas dinner, I cooked for 12 adults and 2 children!
Dd2 was only 10 weeks old and still BFing!! Dd1 was just 5!!
It went surprisingly ok, I did a turkey crown, gammon joint, beef joint and a three bird roast, then roast tatos (goose fat) mash, carrots, parsnips, peas, Brussels, yorkies, pigs in blankets and braised red cabbage.
I also did a nut roast for vegetarian (except chicken and fish) SIL 
Timing was key. I prepped as much as I could the night before, and DHs job was to keep everyone out of my bloody kitchen and their glasses sufficiently topped up!!
I did homemade celery soup and croutons to start which was a hit, and I made sure that the dishwasher was on a quick cycle and was emptied immediately so I could refill it and not end up with mounds of crockery everywhere!
For serving, I got everything in to serving bowls, meat platters etc and then served it all carvery style IYKWIM.
Desert was cheesecake, Xmas pud or trifle, followed by coffee, mince pies and cream and after eights.
I was amazed I did it to be honest!!! Nobody died either 
As for tables, I have two ikea jokkmokk tables - both four seater. I have them together in a long row as an eight seater, or together in a square as a six seater. Cheap and cheerful at £90 each for table and four chairs!
Oh can I also mention, it's my birthday on Xmas day too

Never quite sure how I got that gig!!!! :)