I think they look really neat! all of them! but I do think that if you want to do illustrations is better if you stick to just one style and in a sense "standardize" the design of the illustrations.
For example the third picture is more vertical than horizontal and it feels like it's really breaking the rhythm of the page. I would suggest trying to keep most of the pictures more horizontal, like the second and fourth picture.
I also think you don't need that many illustrations on a page sugar. 2 is fine for that amount of word count!
I hope this helps in any way! - I am very interested in this topic because I want to add illustrations to my story too D: thanks for making this question first~~~~~hero!