I would add a roller shade to the window. Then, I would use sheers to cover the three windows and fuller curtain panels on either side. I would also take your rod a bit higher than it is now.

Can you move the bed to the other wall (under the window to the left in picture)? Then you could remove trim from the two non-windows, patch it up, and just have the one window on that wall to work with.

I would have mirrors cut to fit in the fake windows, then hang sheers over all three, with regular draperies on the sides to close if needed for darkness. Or just leave the sheers and put a roller shade under them to use on the real window when needed.

Maybe some shutters or blinds and subtle daylight lighting to create faux windows under drapes.

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I think the best option is to use aktillery9 or deco's suggestion.

I would treat them as if they were still windows, with window treatments that would just never be opened. Could be curtains, shades, shutters, but the only one operable would be the one on the right.

I'd probably do 3 separate shutters and just leave 2 of them closed. The cleanest and easiest solution I think. Drapery panels would finish it off nicely.

I think Miz_G's suggestion to remove the trim from the two boxes, repair the wall and have only one window makes the most sense. It's strange that the previous owners left the trim when they removed the windows. Put an attractive shade on the one window and a piece of artwork where the old windows were.

Omg, that is so bad. You need to dry wall over all three of those windows and remove them.