This is a very interesting idea! My concerns are essentially the same as yours. Bespoke tempered glass would be great, but crazy expensive, and it would need far more, in the way of mounting - and you still wouldn't be able to open them, at all. If there are only 1 or two that you'd want to be able to open, you could - with the indows - leave the one out, or just pop them in and out as needed, or so it seems. If you go that route, it might be best not to divulge the plan to them, if they're so persnickety about the insulation.
A Christian & devoted Patriot, wife, soap maker, herbalist, formerly a homeschooler, baker, truck driver, and more. I was born in the South, but actually grew up around the Great Lakes. Both of my families had big, lush gardens,& preserved everything they could for the winter. I carried that into my own life. But, change happens and for over a decade, it just wasn't an option. Now, retired in the Ozarks, on 29 heavily wooded acres of mostly ravines, our best crops are nearly inaccessible wild blackberries, rocks, wild herbs, and ticks. We're utilizing our burgeoning small-livestock collection, straw bales, raised beds, and containers to build soil, and a better, healthier life for ourselves and our beloved critters, who provide us with eggs, meat, milk, fiber, fertilizer, tick control, loads of entertainment, and even help turn the compost. 
