All are kinds of pasta.

Wiggle, land, mallow

All are types of marshes.

White, Milk, Dark.

All are types of chocolate.

Election, prescription, conquest.

All ways of obtaining power

Marshwiggle, Centaur and Faun

They are all non-human creatures in Narnia! 

Brush, roller, and spray. 

All are types of paint.

Jadis, Ramandu, the Lady of the Green Kirtle.

None of these characters, good or bad, are native to Narnia, itself, as far as I could see.

Jadis comes from the world of Charn, Ramandu is a retired star, being rejuvenated, whilst the Lady of the Green Kirtle comes from Underland, from whence she planned to invade & takeover Narnia.

Lady of the Green Kirtle, Helen, the Cabby's wife, and Swanwhite 

Three lesser-known beautiful woman of Narnia! (compared to Susan, Jadis, etc.)

The British Consul, Jill Pole, and the process of skin-changing.

All are people or things discussed in connection with Eustace.

Andrew Ketterley, Jadis, Bree.

All three are described to be cowards.

CS Lewis, JRR Tolkein, PG Woodhouse, (EM Forster, HG Wells, TS Elliot, etc. etc.)

Hmm... well these men all have a couple of things in order (1) All known by their initials and surname (2) All of them are male authors (3) All of them lived during a similar time period - end of 19th century to around mid 20th century.

Rabadash, Eustace & the dufflepuds.

They're all male characters who are taught a lesson in some way

Lion, Cheetah, Tiger

Cats!!

A two dimensional space, an incomplete alphabet, and Rachel Lynde

HINT: what axis isn't in a 2D space, what letter is left out if we only say most but not all the letters (english alphabet!), what is Lynde's (Anne of Green Gables) defining characteristic?