Hoshi KLARA wore this dress and mainly stuck around Molly, Miss Rogue, and any of the other kids. She will take a moment to congratulate Tony and Pepper in a very serious tone. She isn't keen on dancing but has no problem enjoying the food.
CLAIRE attended and wore this dress. She attempted to be more social and only cracked a few horrible science jokes.
GEORGE arrived and is basically dressed like this. He will socialize and interact with a lot of people. The easiest way to keep distracted is to go to a wedding, amirite?
HARRY isn't big on huge parties or such things, but he did sit through all those wedding shows with Eleven so he feels like he has to attend. He wears this with his normal eyeliner, black nail polish, and various jewelry, and boots. The tie is going to vanish at some point. He is up for dancing and such.