This is one of those stories that is basically "Aww, this is so cute as long as I don't think too hard about the actually kinda messed up things in it"
That pretty much comes with the "cute yuri monsters" territory, doesn't it? If they're really monsters, they aren't cute, and romance is . . . out of the question.
So, as with so many things in life, it's best not to think too hard about it.