These charming story sketches are by Bill Peet. (Not 100% sure about the last one.)
Peet's work was an animator's dream come true. He worked out story continuity, character relationships, where the camera was placed, and of course dynamic poses with tons of appeal.
Word has it that he felt the need to re-draw Bill Tytla's animation which he considered to be off model in some scenes.
This might be an animation history myth, but you can see in his wonderful drawings that he had a knack for drawing Dumbo as well as the other elephants. Such a great feel for the type of staging that reveals personality.
When I met Peet late in his life, I knew I was having conversations with an animation giant.
More on Bill Peet's work on Dumbo here: