A Sudden Wild Magic (Literature)

A novel by Diana Wynne Jones. A team of mages finds it necessary to invade an alternate universe.

Tropes include:

Aerith and Bob: On all the worlds. On Earth, we meet Gladys, Maureen, Amanda, Judy, Helen and Roz with Zillah and Flan as the outliers; men from the Pentarchy have surprisingly "English" names like Lawrence, Roderick or Edward while the Ladies of Leathe in the Pentarchy are called things like Marceny, Aliky, Ladry and Sigry.
The Alleged Car:
- Tony's Deux Chevaux, which Tod mentally labels a "subcar".
  It was small. It had a domed top, like the head of an amiable but stupid dog, and a curious posture, down at the front and up at the back, as if the stupid dog were engaged in sniffing the gutter; and to make it more remarkable, it was not one colour but several random ones. The domed top was orange. One flimsy-looking door was green. The down-bending bonnet was sky-blue. The rest was a rusty sort of cream. It was like a jester—or someone's idea of a joke.
- And the Celestial Omnibus is pretty much The Alleged Interdimensional Spaceship - cobbled together from an actual old bus.
Baby Talk: Marcus, Zillah's son. Rather observant and smart for two, even though his words hardly make sense to anyone but Zillah.

Can't Get Away with Nuthin': any kind of sexual activity is punishable by exile on Arth, even kissing.

Elseworld: Earth, Arth, and the Pentarchy. They even have alternate selves called Analogues.

Henpecked Husband: Mark tends to question from time to time why he married Paulie.
I Choose to Stay: After the congo dancing scene, the women decided to stay in Arth.
The Infiltration: What drives the plot; realizing that another world has been forcing Earth into war after war to force them to build new technology and copy it, Gladys sends a team of highly trained female mages (as well as Zillah, by accident) to the other world and stop them.

The Mole:
- Brother Tony is assigned to spy on Paulie and return information to Arth. Later, because Tod kissed Zillah, he has to fill in, much to his displeasure.
- For a different faction, Aliky is a plant among Lady Marceny's women and secretly working against her.
Never the Selves Shall Meet: When they enter the alternate universe, all the ones with counterparts there instantly die.
Offing the Offspring: The Big Bad Lady Marceny has absolutely no problem with the idea of sacrificing a grandchild.
Our Elves Are Different: it's hard to define what makes someone a "gualdian" (even Philo is vague, and he is one) but the men are tall and "rather furry", and the women look entirely human but are ethereally beautiful. Gualdian blood is associated with high magical talent, and prized. It's implied we have them on Earth and don't know it; Zillah is identified as one.
Pimped-Out Dress: The Ladies of Leathe wear rather elaborate outfits.
Pocket Dimension: Arth. Though its inhabitants are from the Pentarchy it's a separate miniature universe, and travel between the two can only happen at specific times.
Really Gets Around: Roz. How much of this is true and how much is rumour and propaganda? Unclear.
Sex Is Evil: In-universe. It's not allowed in Arth because it will upset the balance.
Sex Is Evil, and I Am Horny: Not uncommon, though acting on it risks punishment by exile to Earth.
Sharp-Dressed Man: Tod, by Pentarchy standards, though his hairstyle looks pretty odd by Earth standards.

Single-Target Sexuality: Two examples - Judy for Edward and (surprisingly even to herself) Zillah for Mark. Nobody else has a look-in.

Three Faces of Eve: The chief witches of Britain are Maureen (young, a dancer), Amanda (mother and university lecturer) and Gladys (grandmotherly-looking, eccentric Crazy Cat Lady). Played with slightly: Maureen's no maiden or innocent, Amanda has many facets to her other than motherhood, and Gladys may act the crone but is neither as old nor as dotty she seems.