My daughter seems to have raised her kids with the rule I made up:
Whoever sets the table decides where everyone sits.
When my husband came home with the other two, the eldest had complaints. She preferred a different wine cup and wasn't very pleased with her location. The two girls began fighting it out, verbally, of course. I decided to change the rules. I went into the cabinet which contains all the wine and shot glasses and took out a few others, very different from the one they were fighting over.
Success! Each one fell in love with a different cup from those included in my new choices.
"From now on, this is the only wine cup I want!" They said in unison.
That's all it took. And neither of their choices is actually a wine cup. One is a very kitchy small glass decorated with gold swirls and the other is a very modern shot glass, "v" shaped on a blue ball.
Yes, classic "out of the box" thinking saved the day, B"H, thank G-d!