If you are feeling guilty about those you didn't invite this time, why not have another evening with those folks, perhaps just after xmas. In my ideal world I would have a circular dining table to seat a lot of people and that would need a very large dining area,but at least no one gets left out on the ends. I suppose a remedial solution for the present for anyone doing a sit down meal would be to borrow a couple of those round plastic patio tables that seat 6/8 people and cover with some nice cloths and decorations and place fairly close together. As regards a buffet in France, I have to say that it just isn't their way of doing things, everyone wants their own table place,plate,cutlery and glass and be able to natter to their friends. Anyway I hope you enjoy your evening and don't end up with too much work.