I have read the books as well. The writing style is not my cup of tea. I think that under 12 is probably too young for some of the content (especially in the last book). However, there are some positive qualities about the book (spoiler alert if you haven’t read the books and want to be surprised). One positive thing is that it is a story of good versus evil. The main vampire family, the Cullens, fight what is in their nature; they choose to only kill animals to survive. They do not murder people though it is in their nature to do so. They value humanity. There is also a love story, of sorts, between the two main characters, Edward and Bella. Despite the modern literary trend, they choose to wait until after they are married to have a sexual relationship. That is positive too.
In my opinion, the author wasn’t original at all in her story development of the story… boy meets girl, they fall in love, but they can’t be together, he leaves, she turns to someone else, blah, blah, blah.
There is some mention of God in the books. Edward believes that by becoming a vampire, which was not his fault, that he cannot go to heaven if he dies. He does not want Bella to become a vampire because of this belief. But, ultimately, he lets her become a vampire because she is going to die in child birth. Other than that, I don’t believe that God is discussed, and there is nothing about Christ.
I would categorize these books as mythical or fantasy, but not occult. That is just my opinion, of course. But I think of “occult” as some secret revelation of supernatural power in the spiritual realm (God or angels or demons). These are just mythical creatures (vampires and werewolves). Additionally, the OP had a concern about the books being erotic. I would not consider the books erotic and the kissing “scenes” and sex (fourth book) is not written in graphic detail. However, it may be too much for a 12 year old.