Yuuki: She's not likely to change much. She's been fairly stressed and high strung lately, though, so she'll be more relaxed. It'll be a bit more similar to how she was before all of the stuff happened with Kaname back home. Like Ai, she'll have something to make it so that the sun and heat don't bother her at all.
She may be more prone to indulging in food and bloodlust. But blood drinking is most likely limited to family.
Kija: More chill than normal. He's sort of prone to enjoying the finer things in life, so he'll really appreciate the relaxing environment. I'm amused that drugs are a thing, and think it would be hilarious if he accidentally ate/took something that would affect him.
Otherwise he probably would have a few drinks and enjoy the time spent with everyone. (Warning though, he gets drunk super easily and all loopy. In a drinking competition he passed out before the princess did, so... he'd probably be down for the count fairly quickly. He's easier to sway into things while drunk.