We put a bean bag in ours - would that work for your boys?
Re. curtains - we used net curtain wires for the curtains to hang on. I hemmed rectangles and then used plain ribbon to make tab tops to hang them from.
I added an old ship's bell on a rope as the door bell.
You can buy stick on, battery operated lights for the inside.
We also store all dd's musical instruments in it (tambourines, whistles etc.) so all the noise stays outside!