Adult child moves home for awhile

Submitted to Community Café

My adult son has moved home for awhile, while I am recovering from a series of illnesses. This is both a blessing and a curse. We have downsized since he has left home.  His sister has adult onset of schizophrenia and is living with us and had to give up her room so he could have space.

The problem is her room had, for no known reason, an opening that overlooks the first floor. It is about 70 inches wide and 48 inches tall. On one side I had brought a canvas and covered it with fabric so you could not see into her room when you entered.

We are not used to keeping TV down, etc.., The problem is now noise. so must cover from inside. I bought four sheets of  Office Depot® Brand Sturdy Board® Foam Board, 40" x 60", with the idea of gluing them together and letting he and his sister and paint any way they wished. I did not realize polystyrene  is not the same thing as wood or canvas. I wanted the insulation properties for sound.

Have found the right adhesive, now need to find out if I should cover with canvas, and if so do I frame the pieces and add a back brace? and then paint them, or can I paint them as is, or do I have to first cover with glue or gesso... 

I find conflicting advice online, so please any ideas will help.