@Matt4845 That's a really gorgeous listing you have there! Your descriptions are thorough and well-written, your photos are beautifully lit, and the reviews so far show that guests have been super happy.
But ok, I can see one obvious reason that bookings are slowing down after August. Your listing is completely optimized for summer bookings, with its front-loaded focus on the pool, and that's worked out well. But even though there's still more hot weeks to come, when people are looking ahead to their plans for autumn and winter in the Catskills, they're not thinking of cooling off in the pool anymore. They're thinking quiet, warm, cozy. This is a good time to gradually move those pool pics to the back of the queue until next spring, and start foregrounding the Hygge elements of the cabin more. Show off the fire pit, and pull in a shot of the patio swaddled in autumn color. Your minimum stay automatically rules out the casual/spontaneous weekenders (for good reason), so most of the people left in your target group have already squared away their September plans. You've got to be a few steps ahead of them.
How to deal with disrespectful guests? Leave Instant Book off. Those people tend to reveal themselves early enough in the conversation that you can simply decline them.