Mel's Siri of course attended, with Obi-Wan, and likely anyone else from the Temple who wanted to attend. All she knew was to not wear white or black, as that would offend local customs. She wore a purple dress that seemed a safe bet. Her mask was a lavender one she'd picked out earlier in the week when she helped Dan find one.
Iroh doesn't know either the bride or groom well, but he loved a party, loved weddings, and also had to keep an eye on his kids. He definitely did some fire tricks for the guests.
Diana and Poe did not attend, Diana because she doesn't know them well, and Poe because he's part of the hotel!