I have had the same problem with my thoroughbred, I used Hilton Herbs Tea Tree Cream to soften the scabs and keep the skin supple. I have also used the Dermolene Soothing wound cream which also forms a protective barrier for muddy conditions.
It looks from the pics that your horses hooves are very dry and from my experience using Kevin Bacon Hoof Dressing regularly on the outside and underneath the hoof could help.