The elf girl is in Sonia's house/orphanage in the slums of the Royal City, while the book is at one of the shops. I haven't played the current build of Seeds, I'll edit this if this is now wrong
how do I get to properly talk to the neko girls resting in the open bath in the pyramid? equipping both Dancer Clothes and Royal Neko Belly Stud to the person going to interact to the two didn't work
Honestly, it might be because I imported my .400 saves to .410. I'll try to see if this is the case and do a clean slate .410 run to confirm it. Just need some free time to do so.
For now, no, you can't get both of them to 400 power. Maybe in the next update, we will get their cap raised to 400. But for now, again, no. Leah is the only char for now that can reach 400 power.
(Edit) So far I have found 2 locations of Rare Milk Fruit, one being accessible after defeating the Milk Dungeon, and one in the Overgrown Temple entrance, where you need to enter the house with a bridge at its roof. I will update this if I find more.
First, you need to get the Elven Book from the shop at the Royal City. Then, go to the slums and go to Sonia's house. You will find an elf there that will trade the book for an Elven Dictionary. Once you get the dictionary, you can now go talk to the elf girl.
As far as I know, the blue crystal is the only crystal there. You need to impregnate the school as Valorie (you can do so by playing as her at night) by placing Divine Seeds in different locations.