No matter that you have two levels, they will all try to roost in the same spot if they're all in the same run. I don't see how you'd manage close to 26 feet of roosting space in that upper level, especially since it doesn't have much clearance (height). But to answer your question, no, there is no way I'd shoot for 26 birds in that set-up, even if they were bantams.
Even if you free ranged from dawn till dusk, due to your location/winters, you birds would spend a lot of time inside the sheltered (walled) section, and you would have serious problems on your hands (seasonally). Even with a large run added, and with cold hardy breeds, 10 is the maximum I would shoot for in your set-up. Folks who live in year-round mild areas can get by more easily with cramped quarters, because their chickens really aren't inside the coop except for egg laying and night-time.
It is a cute set-up, but if you want happy, healthy birds, then think smaller flock.