Generally pianos are located on interior walls and fireplaces are located on exterior walls. It's important to design the room so that the sitting area can view the fireplace, any entertainment unit such as a TV and a view to the outside.

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Scottscreativehome.com

Difficult to tell with the pictures. Looks like you should move the sofa closest to the tree (on big wall) to in front of the big window in an L shape with the matching sofa. Place the TV (with the fireplace under it) where the sofa on the big wall was. The two chairs should face the window and start just out from where the TV is now. Get a table and lamp for in between them. That should leave enough room for a piano where the extra sofa is now. Turn the dining room table to run the same way the big window is with the buffet console on that long wall. Move China cabinet out to center with end of dining table.