The damage most likely began under the thick profile blocks, by to much heat of the rubber on the innerside under those blocks. courced by to much deflection for the speed you drive,wich on its turn courced by to low pressure for the load on tire.
The cracks in the thinner spots, so the grooves in the profile and the side of the tire only in the profile-blocks, are probably because the rubber under the block was pulvered so had no construction there.
This gives more force on the thinner rubber .
Your last picture also indicates that the treath beneath the profile blocks on left side already came loose.
So If you have your new tires, review the needed pressure for that.
I can help you with it if you give weighed load per tire , second best weighed axle loads , but in lack of that GVWR or GAWR.
Special trailer tires can do with a bit lower pressure so more deflection ( 1 or 2 psi ) because the treath is thinner so isolation of those important rings of the tire , that produce the most heat, is a bit less then a LT tire .
So the thinner rubber parts of tire, where you see the damage , most likely have a intact rubber sturcture.
The real cource of damage you will only see if cut a slice of the tire , as soon as you replaced them ( not before:S)