Q.How Much Can I Cut Back
I just purchased a cattle farm and found an orchard of mayhaws. Approx 20 years old and around 125 trees. They are totally out of control with some oaks and pines growing in them. My question is can I cut these mayhaws almost like you will do with an overgrown Crete myrtle? See attached picture

Certified GKH Gardening Expert
You wouldn't want to chop them in half like many people do with their crape myrtles (crape murder). Mayhaws are usually pruned to open up the canopy. You can remove the suckers coming from the ground that are branch size now. Here is more on pruning mayhaws:
https://www.gardeningknowhow.com/ornamental/trees/hawthorn/mayhaw-pruning-tips.htm
https://www.gardeningknowhow.com/edible/fruits/apples/pruning-apple-trees.htm