No keyboard cases are compatible with the iPad Leather Folio Case. Any case covering is incompatible with the Apple iPad Magic Keyboard since it magnetically attaches to the iPad's back and completely covers it.
iPad Pro 12.9" Leather Folio Case (5th & 4th gen) : https://oxaleather.com/products/ipad-10-2-leather-folio-case. iPad Pro 11" Leather Folio Case (2nd & 3rd gen) : https://oxaleather.com/products/ipad-pro-11-leather-folio-case-2nd-3rd-gen. iPad Air 1
Yes, they do. And the kickstand mode of the iPad Leather Folio Cases makes reading, typing, and streaming simple.
No, neither the iPad nor the iPhone is affected by the magnets in the Leather Folio Case. Apple created the iPad Pro and iPad Air to work with the magnetic elements of its covers. The same goes for iPhone.