Here's another picture showing the opening into the room

You didn't say what pieces are sentimental, so I'm guessing the clock. However, I would rather see it in an entry foyer. Pianos need to be placed on inside walls, so you may want to switch it and your sofa position. With new shutters, a sofa can work well in the window with two smaller armchairs flanking it. They can float and face each other over a new coffee table, or together with their backs to the big opening. Just keep the scale of your new pieces small. That will leave room for the curio to go where the piano is now.

What is this room used for? Is it the pretty living room for company?

looks like your going for a more traditional look.... I love that, its rich looking and full of taste. THe first thing I would start with is the carpet, and the curtains to be replaced. Keep the chairs. They are beautiful! The sofa can easily be re-upholstered to a rich velvet, maybe brown or in the nuetral color scheme. My mom searched for a couch for ages and than decided on reupholstering an old couch that was sitting in the basement. You wouldn't believe today that it's 20 years old! It look s BRAND NEW! Also I would get rid ot the lamp and picture ontop of the sofa. Put the sofa on the wall of the piano like that when you walk into the room it's the focal point. The chairs should go facing the sofa and the piano where the sofa is. You can use a new coffee table as the one you have looks old. The clock should go left to where you walk in.

heres another idea https://www.houzz.com/photos/library-traditional-family-room-san-francisco-phvw-vp~55795

This is indeed the "pretty room when company comes". The clock and curio cabinet were made by my husband and the piano was bought for me by my mother many, many years ago. I don;t know how she afforded it. I can't bring myself to part with any of these three things. I have want to put the clock in the entry way and could also use advise on that. I don't really like the chairs or the sofa and the coffee table is just waiting for someone else to take it.

beautiful entrance to the room. I find people that like lace want some lace. Your lace fits properly. It needs a cornice along the whole top to pull it together. I agree smaller scale chairs and sofa. Soft pink and cream . Maybe paint the arch in deeper trim color.