But I couldn’t find a credible source for the “showing children pornography” portion you mentioned

It's from one of the kid's testimony in the first link (it starts with "Now, when you first saw the suitcase, where was it in that room."), where he talks about how Michael showed him and his brother some porn mags. The first time he was hanging out with MJ while he was putting on makeup, and MJ picked up a suitcase with the porn mags and showed the kid one of the pictures. In the second occasion the kid can't recall if he or his brother brought up the suitcase or if MJ did, but he says that they were all looking at the magazines together for "30 minutes to an hour".

Regarding the books specifically, it's one of those elements that on their own could be interpreted as just MJ being kinda weird. We know the first book was a gift given the fan's inscription, and it's fairly reasonable to assume that the second one was a gift too. As the blog post points out the third book wasn't brought up in court and wasn't with the other two books, but it's still reasonable to assume that it belonged to MJ. To me the way the blog author tries to "soften" the book definitely points to some bias in their part:

The third book, that was confiscated in 1993 In Search of Young Beauty: A Venture Into Photographic Art (Charles Du Bois Hodges, 1964) which contains both boys and girls, mostly dressed, but some nude or semi-nude.

If we squint a bit we could just chalk these up to MJ possibly being a nudist or being a bit weird. I certainly think it's odd that he had books with pictures of nude children in them, and even liked one of them enough to inscribe his own message in it, but if only the books were brought up in court I certainly wouldn't think that's enough evidence to convict someone. But given the whole context and other elements of the accusations I'm not willing to give MJ that much benefit of the doubt.