I found a mod which adds the books from Daggerfall to the game but is there a mod that adds the books from Oblivion, Arena, Redguard and Battlespire? I can't find anything like that. Surely someone must've done that in the past eight years.

Actually, as you probably know, it is illegal to use resources from other Bethesda games.... and this does include the text in the books introduced by other TES games.
Yes, there are mods that add MW books to OB, and other such mods... but they are technically not allowed.

it's illegal to copy text?

There was an instance a few years ago where Bethesda stepped in and removed a mod or two from PES that used OB books in MW.
One can assume the same restrictions apply for all TES games.

Some mods do exist that defy this rule, but it's likely just due to Bethesda not knowing or not worrying about such small matters in certain situations.

Well that certainly is a load of horse road apples. I guess there isn't a mod that does that then. I suppose I could do it on my own. I have lots of book covers by Korana for Pelagiad Expanded and I want to use other stories from the games for them.

If you search PES, you will find at least two that bring modified versions of Ob books in. I'd have to search my stash to find the exact ones. There is also the TES Imperial Library, which also has a lot of books and text resources from all of the TES games - going back to Arena and Daggerfall.

Keep in mind, a lot of Ob books won't make sense time-wise, or will have been written after Morrowind is long past. Be careful to read anything you use after Morrowind to prevent putting in built-in spoilers. For example, one book details the adventures in Solsthiem - well after the player is gone. I'm using one of the book mods myself, and I've had to carefully edit, or delete, certain books that get too close to being spoilers. Daggerfall and Arena texts should be fine, though - those events occurred a long time before Morrowind was set.

Yes, it is technically an issue, but so far Bethesda doesn't seem to have a problem with mods that only bring in text - as the book mods I mentioned have been around for ages, and are still on PES. I've also seen Ob books in quite a few house mods as well, and Silgrad tower brings all of the books from Morrowind into Oblivion. However, you have been warned that they *might* have an issue with it.

The difference between Morrowind and Oblivion is like six years (That is for the main story, with the expansions and stuff the time-lines run right into each other. The time of Morrowind is 3E 427-432 while Oblivion begins in 3E 433.), I doubt that most of the books in OB were written during those six years.

Huh.. I didn't realize that the books in OB were game-wise written recently. I thought they were books that were written by authors decades, maybe even centuries, ago. And they were just more stories that the devs thought up to add to the game. Ya know, kinda like the equivalent to our books by Charles dikeens and stuff.

I just went on TIL and realized that there are not any books at all in Arena. Is that true?

I didn't realize that either - but a lot of books refer to events that are essentially spoilers. These books would be a bit hard to explain in Morrowind, prior to their occurring.

I'll just stick with Battlespire and Redguard books to add to PE. I mean, name just one mod that adds those books to the game.

Sure, but there are some really good books in Oblivion you will miss. I still like reading the Argonian Account - the sequel to A Dance in the Fire. I made sure there were copies in at least two places in Ravenwood.

Well, if the book has spoilers or doesn't fit the Morrowind game, then I won't add it.
What I'm also looking for are children books and stories and nursery rhymes. I'll probably stop over at the fanfic section and see if anyone has or can write a children's story.

Just avoid revised history books. In most cases, it's fairly obvious.