I know this is really old but OH MY GOSH! i COMPLETELY AGREE. I've been a part of the fandom for a few years now, and ever since 2018, I've been making fanart and reading the books ever since.
And as mentioned above, it really doesn't seem like a kid friendly book franchise. Yeah, it's got cats and stuff, but it mainly covers mature themes.
Basically the books follow a story of four clans(which is just a large group of cats) who are enemies, but they have to live in the same forest with eachother. (they have their own territories of course, but sometimes this creates conflict)
So anyways, this franchise covers violence, detailed lore, romance, adventure, mystery and all that good stuff. I've read a few books already, but now i'm able to read them for free online.
It's this website called Bookshare. Doesn't give me the vibes of reading an actual book, but at least I can catch up on the books.