E8 type thoughts.

Current standings:
Mr. Luck - (Any type Combination) - Any Field
Hendrick - (Steel/?) - Collosseum
Hazel - (Ice/Ghost) - Snowy Mountain
Kai'ya - (Grass or Psychic/?) - ?

Jolene - (Electric/?) - ?
Dylan - (Water/Poison) - Swamp
Karen - (Rock/?) - ?
Tesla - (Fire/Dark) - Hell

Types left over:
Fighting
Ground
Dragon
Fairy
Flying
Bug
Normal

Possible Combinations:

Hendrick:
Steel/Fighting
Steel/Bug
Steel/Ground

Any of the three secondary types can work with Colosseum, field is mostly themed around Fighting, Dark and Steel types but isn't particularly negative for others, Bug in particular has a surprising set of buffs, whereas Ground just covers well for Steel's weaknesses.

Kai'ya:
Grass/Psychic - ??? Field.
Grass/Bug - Flower Garden
Psychic/Fairy - Starlight Arena
Grass/Psychic or Grass/Fairy - Starlight Arena
Psychic/Ground - Ashen Beach

Unsure about this one, No field particularly accomodates for both Grass and Psychic well. Psychic/Ground COULD work on Ashen Beach possibly. Not huge on it though. I GUESS there could be Bewitched Woods or Grassy Terrain under the Starlight Arena and go Grass/Psychic? Plenty of Grass types get Nature Power to take advantage of the field boosted Nature Powers. Some get Moonlight and Wish which is good here. Starlight is also particularly notable for Hoopa since it's signature moves get MASSIVELY buffed, with both hitting 3x their normal power!

Jolene:
Electric/Flying - Mountain or Sky.
Electric/Ground - Factory/Shortcircuit
Electric/Fairy - ???

Mountain and Sky are iffy due to being practically identical to Hazel, and having a large variety among the E8 is preferred. If Hendrick didn't have Steel, Electric/Steel on Factory would probably be amazing. This is the one I'm personally most lost on. There just isn't anything outside of Sky that really works for her. Underwater would work but Dylan is already the Water expert and without Water types, Underwater falls flat IMO.

Karen:
Rock/Fairy - Crystal Caverns
Rock/Dragon - Dragon's Den
Rock/Flying - Mountain
Rock/Fighting - Rocky Field

Plenty of Fields  and Types for Karen to possibly use. Just a matter of what type combination we pick. Personally most partial to Dragon's Den since it works best for Mega Diancie. Mountain works too but as said with Jolene, Hazel having Snowy Mountain kinda makes that hard to do.

Personal Draft:

Mr. Luck - (Any type Combination) - Any Field
Hendrick - (Steel/Fighting) - Collosseum
Hazel - (Ice/Ghost) - Snowy Mountain
Kai'ya - (Grass/Psychic) - Starlight Arena

Jolene - (Electric/?) - New Field
Dylan - (Water/Poison) - Swamp
Karen - (Rock/Dragon) - Dragon's Den
Tesla - (Fire/Dark) - Hell