I would move the desk from the niche and put the tv there and then turn the sofa so that it is facing the tv with it's back to the doors (or windows) on the right and a space to walk through to where the guitars are currently. If that is a window, you can just back the sofa up to it. Then either get rid of the love seat (which I would do) or turn it so that it is facing the black sliders that we can see. Use the rug and coffee table in that area. If you got rid of the love seat, get two chairs with a small table in between them in the same place that I suggested for the love seat. That would be more open and give you a better view of the sliders and outside and yet still define that are as the family room section of the room.

I would then move the guitars under the stairs with that yellow chair so you could sit down and play them. Put the bookshelf from the niche in that little alcove.

I am not sure what to do with the desk. But once you move the tv, you could put a small table with two chairs in the area where the tv is currently.