SOLVED. Middle reader to YA sci-fi/fantasy novel series read in the early 2000s, 2005 or 2007- takes place in an alternate United States where Pennsylvania is considered a wild state with an almost communist, Stalin-like Shadow leader. [s]

[Gabriela]

The main characters are three adolescents - one boy and two girls, one of which is named Lily.
The first book contained their adventure to save a monastery in the alternate Pennsylvania- this monastary had a tiger in the closet. The cover of this first book had the three protagonists fighting a purple jelly monster with tentacles - the boy is holding a ray gun of sorts and Lily, the girl, is being hooked by her backpack. The book itself is pretty long, about 2.5-3 inches thick.
I also remember another book in the series, also about the protagonists' adventures in the alternate Pennsylvania/Philadelphia. The cover of this one is warm toned with a lot of reds and yellows; also, spoiler alert, it depicts a scene from the book where the two girl protagonists are escaping a restaurant fire via riding in a lobster tank. There is also another character introduced, a dashing boy spy with a blindingly white smile and teeth described as chiclets. The main plot is that there is a revolutionary group looking to defeat the fascist like Shadow leader of Pennsylvania/Philadelphia. Towards the end, again spoiler alert, the three protagonists and most of the revolutionary movement are captured by the 1984-ish government and are put on a mock game show where they are interrogated and compelled to confess in front of a live audience. If they do not answer or are defiant, they are threatened to be dropped in to a tank of sharks. The boy spy from before is revealed to be a doublecrosser who works for the Shadow leader and had been instrumental in the good characters' capture earlier.
These are not all the details I remember, so if you have any questions, I will answer all of them.
Even though this series is so outlandish, I cannot find anything about it online, even when I Google the most specific details.
I appreciate any and all your help.

[Sarah]

Do you remember the names of the other main characters?

[Gabriela]

Sarah wrote: "Do you remember the names of the other main characters?"
I can't remember the other girl's but I believe it's a very generic American name. I can't remember the boy's either but his nickname was "boy wonder" or something like that. The monks in both books always have their names beginning with "Brother".

[Sarah]

This is a long shot: A Riddle in Ruby.
I hope you find this book!

[Gabriela]

Sarah wrote: "This is a long shot: A Riddle in Ruby.
I hope you find this book!"
I'm afraid the series I'm looking for has a much more modern setting but thank you for helping!!

[Adele]

I believe the series is Pals in Peril

Here is the book with the purple tentacles (great description by the way - it is exactly as you describe!):

Here is the first book in the series:

The main characters are Lily, Katie, and Jasper. (Jasper Dash, Boy Technonaut)

[Adele]

Oh, and here's the one with the warm colors and the lobsters:

[Gabriela]

Adele wrote: "Oh, and here's the one with the warm colors and the lobsters: "
Oh my gosh, thank you so much!! I've been looking all over for this series!!

[Adele]

You're very welcome. :-)