If it were me, I would put the couch on the wall with one window to open it up more, but not against the wall, float it out a little maybe put a console table behind it with a lamp or two. I would then put the tv on the stairway wall, possibly angled in the corner? You have quite a few options. I know it is difficult when you have such a big room but floating is the key. You can always anchor the space with a large area rug.

You're welcome, my pleasure. I mentioned wall mounting tv on an angling arm, and there are various types of arms available, depending on your needs. 'TV extension arms' would extend the tv out to mitigate the distance, these arms are also available with varying angling capabilities One example: [https://www.houzz.com/products/pdx650-full-motion-mount-for-37-75-tvs-black-prvw-vr~29971748[(https://www.houzz.com/products/pdx650-full-motion-mount-for-37-75-tvs-black-prvw-vr~29971748) This mount would extend tv out about 2 feet, and is pretty streamlined, with tv being able to sit 2'' from wall when mount is pushed back, so that's a nice feature. Just one example, and there are arms that extend out further than this one, lots of options available to suit your specific needs. I like the idea of wall mounting tv on an arm - but another good option could be using a mobile tv console, and if you like industrial styling, at all - there are a ton of wheeled options, in that style category, alone. So with either wall mounting on extension arm, or using a mobile console, your boys should be able to move the tv, versus having to move their seating... although, they could do a combination of both - if it's more comfortable, etc. I love that second light fixture, also. So many fun styles in the Sputnik type of design. :)

It does look like the room where leftover furniture goes because it doesn't play well with others. The china cabinet could be a good focal point as JudyG suggests, but only if you have something to go inside it that's worth looking at. Otherwise, lose the loveseat and put the china cabinet on that wall. Fill it with books, if nothing else. Alternatively, lose the china cabinet and keep all the seating. Add art above the sofa and loveseat, a rug and curtains, and call it done till you're ready to decide how you actually want to use the space.

Another voite to remove the fireplace and hearth. Will you keep a desk area? If so, I would move it to the wall left of sliding doors, put the sofa table on the wall where the desk is now and the sofa against it. A lamp or two on the sofa table. Sleeper sofas are super heavy and sometimes not that comfortable to sit or sleep on. For comfort, a left hand chaise would be nice for TV viewing. With the FP gone, the TV could go to the left a bit and could sit on a small media cabinet. Rig sized correctly and a small round coffee table. ETA: After looking at photos again, I see that is NOT a desk area. If FP is removed, you could use that chest on the "new" wall with the new/smaller TV on top or hung above.