It's pretty much all in the rulebook.
But you are coming closer to the Tippyverse every time your antagonists use spells the way they are written in the Player's Handbook.
Usually the DM dials it back and ignores tactics like this. You've got one, maybe two, antagonists that are epic level (if you are using epic levels).
I mean really. You have characters who casually spam Greater Teleports on a whim, almost accidentally decide to use a divination spell and find the id of an important protagonist ally.
I mean, not only where do Rocky and Lenny fit into all this, but your party is just too low level to oppose these guys without dm fiat to hold them back. And to be honest Julia isn't going to be doing the heavy lifting if and when the party levels up. Angela and Jordie will be doing that.
Okay, other than stupidity, what stops Angelo and the Emperor from using his disguise spell that is proof against true seeing, then paying Merla and whoever she is with a visit in the morning? Thomas Stratus? The only defense seems to be to physically be in Silverfronds.
Just saying that if you are going to use the rules to the fullest extent, and not give characters plot protection, then the only thing that matters are full casters. Not partial casters like bards, and definitely not melee characters.
This game is about full casters period.
In the old days (pre 3.x and 2e even) magic had a lot more limitations. Spells could take a long time to cast, to memorize (maybe a couple days for a 9th level spell).
But even then you have reached the point in this game/webcomic where a 1.x dm might toss out an artifact weapon to Lenny.
And come to think of it, does Rocky even have UMD? He has a high intelligence, he ought to be smart enough to know he should have been putting ranks into it.
But honestly the smartest thing he could do is start taking wizard levels. An 8th level wizard is a better character than a 15th level rogue.
My two cents anyway.