Think about hotel rooms. They so often have a room-width black-out curtain ... and behind it a thin sheer ... and usually some type of non-moveable header (either cloth or wood) ... and they pull open so nicely. While staying in a hotel a year or so ago, I decided that's exactly what I want, so I took a good look at the hardware involved. Hotels have ceiling mounted tracks. Something like this: This ceiling-mounted curtain track can be supported every 2-3 feet, eliminating any possibility of sagging rods as years go by. You can cut them to fit your dimensions, and they're even available in around-the-corner styles. The negatives, of course, are that you'll need floor-to-ceiling curtains, and you'll probably have to do some sewing adjustments to the curtains yourself. Still, I'm going to do this in my bedroom, where I expect to open/close the drapes frequently. I wouldn't do it in, say, the dining room, where I'm going to use plantation shutters and curtains that'll essentially never move.

It’s for a rental. Perhaps you are overthinking it? Generally you need to focus on tenant-proofing. Is this Airbnb or extremely upscale? Furnished?

Why not do the sheers with grommets then opening and closing is very easy. Actually IMO solar shades woulf solve the whole issue use them all day to control heat and light and let you keep the view and give you daytime privacy the the heavy drapes can go on the traverse rod and done .

Between the radiators and no wall space to the left of window D, I would skip curtains and rods altogether. If the radiators are electric, you definitely want to skip curtains. You look to have plenty of depth in the windows to hang blinds or shades in them.