dog that poops specific shapes for evil gremlins

I have a very distinct memory of this book where the family has a pet dog who can poop specific shapes, and there’s gremlins or elves of sorts that pay the dog to poop in their desired shapes. one day the gremlins ask for the poop to be foot shaped and they place the poop on the dads walk to work and he steps in it thinking it’s his shadow. The dog has a dog house with a pile of coins in it from all the money the gremlins have paid him. I think the book was split into 3 parts and in the last part the mom runs up and down the house stairs with the youngest daughter strapped to her chest to help her train before she goes travelling around the world or climbing a mountain or something. I have been searching for the book for years and not even chat gpt can figure this out, please if you have any idea let me know, THANK U 🙌