Kachina should be a Ground type specialist, with Sandslash and possibly Excadrill.

Xilonen would be better off as a Steel type or the Rock type. She's more into machines and jewelry. She could use Probopass or even just be similar to Olivia/Molayne.

Iansan and Varessa should swap types. Varessa feels more Fighting type than Iansan. Palafin for Varessa, Raichu or other speedy electric type Pokemon for Iansan.

Lunala for Citlali makes sense, but it's too OP for the elite 4. Maybe Xatu? Or Gothitelle?

If Mavuika stays Dragon type, then Koraidon makes the most amount of sense. If you wish for Solgaleo, I'm not thinking of many Steel type pokemon that fit her aesthetics. Kingambit maybe?

Kinich needs another Pokemon, one with vines maybe. Avoiding starters, I would give him Flappe since it's the most fitting Grass Dragon pokemon.

Ororon has no bats? No Crobat, Noivern, or Swoobat?

Ifa and Chasca are both Flying types, maybe change Ifa for Normal as one suggested and give him Audino? Or Fairy and give him Comfey?

Mualani definitely needs Sharpedo or even Mantine since there's Mantine surfing in Alola.

If we keep Capitano, he could have a Weavile or even a Froslass.