Well, I downloaded your mod and played around with it for a bit. I was able to pass through all of the windows - and that’s also a problem, since I was able to pass through them from the outside while they were closed, too.
Also, (o)pening a double pane glass window with a curtain from the inside will turn it into a double pane glass window (without curtains).
By the way, the movement cost of the windows are set to 50, which makes it faster to go through windows than to walk on the ground (100).
Is it intentional that you can’t open/close the curtains once you placed them (on all other windows except double pane)? And to be able to see through them anyway (again, all windows with curtain except double pane)? And the double pane window (with and without curtain) is the only type of window you can (try to) pry open…
Then about the bathroom windows (frosted glass): Sadly, I don’t think there’s a way to reduce or distort the vision through a terrain tile (other than blocking it completely) using the json file. You need to do this in the source code of the game or hack something together with lua (edit: lua support was dropped some time ago and I missed that change)…