I'm not sure if you have enough roost length or not. 8" per chicken is the minimum recommendation for your sized birds. I counted 10 chickens and your coop is probably 8' long, so you should have enough. If you have the roost length, I'd suggest putting a top of the nesting boxes and lock them out when they finish laying. Make it slanted to keep them off or with enough of an overhang that they can't mess the nest.
If you don't have enough roost length, it gets trickier. It looks like you are feeding and watering in the back of your coop, so you don't have room to add more roosts back there. Some things to think about. Possibly move your nesting boxes outside the coop and provide more roosting area. Your climate will determine if this is feasible and how you would design them. Or consider feeding and watering outside to free up more room for more roosts. Again, climate will detemine if this is feasible.
A more radical possibility may be to move the nesting boxes under the existing roosts and put enough of a top so they don't mess in the nest, locking them out of the nests until they are retrained, and providing more roosting area where the nests now are.
The one I'd give strong consideration to is to put a top on the nesting boxes, extending out far enough so they can't mess the nest from above, lock them out, but make sure they have enough headroom to roost immediately above the nesting boxes or preferably out more toward the middle of the coop. You may need to scrape the poop off the top of the nesting boxes more often than you want to, but that is good concentrated nitrogen for your compost heap.
Hopefully, someone will come up with better suggestions. Good luck with whatever you decide.