Shiro will carry around a colorful drink and try to make sure everyone's comfortable. Kosmo will probably trail after him sometimes because Shiro is weak and definitely fed him scraps of party food?? Lmao. He won't stay away from Keith and Lance long and he might need the occasional knock to get out of watchful protector mode, but after like his third drink, he'll be soft and hug on all his friends.
Noct is coming with Gladio and Ignis and Umbra and probably Henruit too. Umbra loves the beach and is messenger of the gods smart so he'll clue into it being a celebration of Lance pretty quick and visit him a lot. Do little tricks etc. Noct is nursing a Pina colada and brought a gift certificate to a food truck called Extreme Eats. He has no idea what the food is but the truck had a giant jalapeno crying on the side and figured that would be Lance's speed.