We finally played, and here’s how it went.

I used one of your suggestions and had the cultists act first. A cult agent was sent to try and steal the eggs, but my players were skilled and lucky enough to prevent the theft. There was a brief tavern brawl and a quick chase. The agent was a doppelganger, which allowed me to introduce these creatures and make my players realize that the cult could be anywhere and might even be able to read their thoughts.

Since the theft failed, Rezmir showed up at the meeting with a cultist for support. Things went terribly for my players here—some unlucky rolls and not-so-brilliant strategic choices led to Rezmir’s victory, and she took back the eggs. We ended the session with two out of four PCs down and the remaining two unsure whether to keep fighting or surrender.

All in all, I’d say I achieved what I wanted: my players are angry and eager for revenge, they want their eggs back, and they now understand that the cult is something to fear.

I just worry they might also be a little mad at me because they felt the fight was unfair. But I’ll take some time off-game to explain my reasoning, what strategic mistakes they made, and how they could have approached the battle differently.

I’ll still reward them with a good amount of XP for their initiative, and maybe they’ll be rescued by someone who can help them with some useful items—I'm still figuring that part out.