This reminds me of something that happened when I was a teenager. My aunt and uncle (mom's brother and his wife) were hosting a family Thanksgiving that included both sides of the family (meaning, the family I was related to through mom/uncle, and my aunt's siblings and their children). In general, this isn't an issue. We have all met my aunt's siblings and their children many times, and we all got along famously...for the most part.
At this particular Thanksgiving, my aunt and uncle had gone to great lengths to set up the table so that we could all sit together. In their basement, they rented and set up an extra long dining table with three extensions put in. This meant that all 16 people in attendance (children and adults) could sit together. Both my uncle and aunt are the youngest of their particular siblings, and grew up hating the notion of a "kids' table," since being the youngest relegated each of them there well in to early adulthood. It was well organized, very thoughtful on their part, and made for a nice familial setting.
Well, that is, until my aunt's older sister showed up with her 8 year-old daughter in tow. Aunt's sister, who I will call Karen, had made it clear that she and her "precious angel" (her words, not mine), would not be in attendance at Thanksgiving. As such, 16 people RSVP'd, and 16 places were set at the table (which was rented to seat, you guessed, 16).
When Karen noticed that there were not enough places at the table, Aunt made a mad dash to the neighbor's house to borrow two folding chairs from them in order to accommodate Karen and "Precious". She then spent 15 minutes rearranging the table, the seating, the place settings, the food, the candles...everything. Karen was not happy still, because that meant things would be too crowded.
Karen then set up folding trays in the living room (upstairs from the rest of the family), for my sister and I to eat at. Since we were the oldest of the kids in attendance (my sister being 18 while I was 15), Karen thought we would best handle eating alone. The other kids, she felt, would be too upset to handle it. Aunt, a normally lovely woman, didn't say a word about it (perhaps out of fear of a very domineering older sister...but, that is just my speculation). Uncle was busy frying the turkey on the back patio (yummy...fried turkey) to notice the commotion inside. And, thus, the people hosting did not object.
When my parents finally noticed what was happening, the family was sitting down to eat (with my sister and I banished to the living room alone). My father asked why my sister and I were put upstairs, to which Karen responded "Oh, well, it would be crowded with 18 of us so I thought it best that they eat upstairs, they'll be fine." Aunt and Uncle just stayed quiet, while the rest of the adults' mouths hit the floor. This was not going to fly with my parents who filled their plates along with everyone else, then stood up with their plates, silverware, and glasses and marched upstairs. When Aunt asked mom what was going on, she stared right at Karen and said "if our children are not sitting at this table, then neither are we."