Luna does have Sableye. Also, Florinia has Ferrothorn at Fiore Mansion. (also if you're going to include Sun/Moon Pokemon it might be best to include a spoiler warning in the thread title)
Julia: Oricorio Pom Pom Style
Florinia: Chesnaught. Spiky moves in desert.
Corey: Salandit. Corrosion. Corrosive Field. Corey's name pun is corrode.
Shelly: Cutiefly
Shade: Dusknoir for reasons you listed, or Cofagrigus because of the eyes
Kiki: Mienshao
Aya: Scolipede
Serra: Alolan Ninetales
Noel: Drampa
Radomus: Alakazam
Luna: Absol. One belief Luna mentions a lot is that darkness is misunderstood. So is Absol. People think Absol cause natural disasters because they appear when they're about to happen, when Absol is actually trying to warn people.
Samson: Machamp.
Charlotte: Alolan Marowak
Terra: Dugtrio
Ciel: Crobat. You can't spell acrobat without Crobat.
Cal: Camerupt.
Blake: Cloyster (was actually his ace for a league season)
Bennett: Beautifly or Mothim are the only two butterflies/moths he hasn't used
Sigmund: Magnezone.
Victoria: Pangoro
Cain: Roserade
Fern: Amoonguss