In the first season, most of the family meals happened in the same room as the kitchen (nook?)
The fancy-dining room made it's appearance in season 1's Wanderlust. The walls were a beige-like color and there's a china cabinet
The fancy-dining room makes another brief appearance in season 7's Ripped. This time, instead of some shelving as it appeared in season 1 (check the photo from Wanderlust just above this one) there were those French doors. The walls are a dark green color
In season 9's Alternate, the French doors seem to be gone, there's also a crystal chandelier and ceiling beams. The walls were white
In the same season (9) but this time in Blinded, the walls are now greenish (lighter than the walls in season 7) and now there's a different chandelier.
In Season 10's Lunacy, the dining room makes a brief appearance. The chairs look different as well as the chandelier. There's also seems to be a china cabinet as there was one in season 1 (more likely very different)
In Season 11's Turmoil, I'm not entirely sure if the room behind Kathy/living room is a dining room or a den?