Free the Familiars!: Constructing a Oneshot

How do you do, my fellow GMs? So my group gathers together for bi-weekly Oneshots (typically three to four battlemaps in length) and I'm trying to put together a oneshot a little more challenging than our usual 10th level party affairs. I could use some help putting this one together, though I've got the basic framework etched out.

Free the Familiars!

A oneshot in which players command low CR creatures that are the familiars of Wizards from each of the main schools. They must escape imprisonment and find their way to freedom, all while putting a stop to the one capturing familiars in the first place. Each of them has a selection of spells from their 10th level masters’ schools, but they cannot regain expended spell slots.

Rewards: Orellia’s Tome of Beast Familiars, Chimeric Collar, Power Collar, Voyage Collar

Enemies: Gremishka/Swarm (They have a taste for spellbooks, components, AND FAMILIARS), Bandits, Drow, Orcs, Thugs, Evil Mages, Bandit Captain (Boss?), Ambitious Assassin (CR 5 Legendary Boss?)

Quattro (Gazer) - A proud and haughty male Gazer who sees himself and his beholderkin as superior to all others. He considers his fellow familiars to be his minions, even if his power is nothing more than smoke and mirrors. As the figment of a beholder’s dream, he can craft terrifying Illusions. He gains Improved Minor Illusion, Malleable Illusions, and Illusory Self.

Aisha/Layla (Tressym) - A matronly and prissy female Tressym whose mistress was an esteemed Diviner. She rolls two Portent die at the start of the quest and can awaken her Third Eye.

Gizmaluke (Pseudodragon) - A brave and commanding male Pseudodragon whose master was a powerful Evoker. He gains the power to Sculpt Spells, Potent Cantrips, and Empowered Evocations, but his cantrips are only 1st level.

Flopsy (Almiraj) - A timid and shy female Almiraj who defers authority to the strongest personality in the room. Her master was a skilled Abjurer, and she starts with a 10th level Arcane Ward and the ability to project that ward onto her fellow familiars. Once it’s gone, it’s gone.

Thimblewick (Imp) - A cunning and diabolical imp who prefers subterfuge and speechcraft over direct conflict. People underestimate him, and he fully uses this to his advantage. He can use Minor Conjuration to create tools to aid in his schemes, and can escape danger or move his allies tactically with Benign Transposition. His diabolist master was an expert Conjurer.

Shovel (Quasit) A bloodthirsty and profane little snot who finds great pleasure in terrifying and tearing apart other living things. Thankfully it’s not that bright and can be easily manipulated with promises of greater debauchery and violence. Its master was the famed Thayan Necromancer, Illyn Toth.

Trixie (Sprite) Trixie is a contrary and huffy little fairy who can sense emotions with her Heart Sight. She pretends not to care, but her empathic senses make it quite clear she cares a lot. She can use her Hypnotic Gaze to run interference while her allies handle more important tasks. Her mistress was a charming Enchantress.

Slurk (Slaad Tadpole) An NPC and known snitch who betrays the team in an attempt to become a full fledged Slaad. His former master’s proficiency in Transmutation will greatly help facilitate his evolution. If he successfully transforms, he will become a CR 5 Red Slaad.

I'm trying to piece together possible battlemaps and encounters, but I'm drawing blanks. Any assistance would be greatly appreciated.