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Since it was never mentioned in all the thread: on the windmill, the individual slats on the 2 upper sails are the opposite pitch from the slats on the lower 2.

Not having the 2 pairs of sails be at 90 degrees to each other will not cause significant problem. As long as each sail has another opposing it, it can still be in balance. It’s unusual and would serve no purpose for a windmill but it would work and i have seen many fans in this configuration to alter the sound and vibration produced at high speed rotation. There’s also a common 7 blade fan designed with completely asymmetrically angled blades that works just fine too. (see attached). The greatest point of instability is when the sail passes in front of the structure at the bottom of the rotation; at which point if its close to the structure, the air flow will be disrupted to go around the building and change the localized air pressure or even direction between the sail and building. The result will be a change in force only on one sail at a time as it passes through the bottom of the rotation, however; in all the centuries windmills have been operating, they seem to deal with it just fine. As mentioned of course, this windmill will strike its stairway thus disrupting the delivery of force from the sail somewhat more.