Re: WHO. Noctis is there with Gladio and also invited Wei Wuxian along too because he was like ooo I love weddings and Noctis has a soft spot for extroverts who take the attention off him. I pretty much hate his canon taste in suits (sorry, Noctis) but this fanart is nice enough so we'll go with that.
Jacob is there with Serefin, dressed in something like this but probably a bit scruffier cause he's stuck somewhere between victorian england and hipster rocker vibe.