When I was in middle school I read it in one night. I was obsessed. It's a moral, easy, wonderful story and is as fantastic as it is fantasy

As a precursor to Lord of the Rings, this IS fantasy, all others are an attempt to reach it

Came here to reiterate the Hobbit

Percy Jackson for mythology(both will love it), shoutout to the Kane Chronicles though, absolute legends

Hunger Games for the older one, SciFi/Dystopia YA

A Wizard of Earthsea for Fantasy

Dragonflight, or The Harper Hall trilogy for the older girl, its amazing Fantasy/Sci-Fi and will inspire plenty of reading.

The Hobbit. The Hobbit. The Hobbit. As a precursor to lord of the rings.

But I really came here to say there are thousands of free digital books that are in the public domain which you may consider adding if you can. Most books considered classics are free in some way, like Moby dick or Tarzan or Wizard of Oz, Dracula, etc. Id suggest getting a collection of Shakespeare's works just for them to be able to poke at when school requires them to read it, and its invaluable beautiful genius works. I'd also suggest for the girl finding a copy of a collection of Emily Dickenson poems, theyre often short and easy to read and poetry needs better representation. Get the younger one a copy of hitchhikers guide to the galaxy, its so fun and it's great sci-fi.

If they're religious or come from a religious family they'll almost certainly be a copy of the Bible, Quran, Hebrew Bible, or other holy texts for free or cheap.