Nico di Angelo
Nico attended solo (ha). Um, he would've tried to find something nicer than his normal threads to show up in (or at least would've done his shirt inside to make it plain black) but probably still wore his usual jacket over it.
If they were doing general toasts/speeches outside of the usual best man speech sort of thing, he would've given a heart felt toast and blessing. Otherwise he would've been wall flowering a lot and probably hanging out down at the beach at random intervals.