I have a similar angled fireplace. If you're not wedded to the TV over the fireplace, I would suggest putting it next to the fireplace and angling your furniture around the TV. That's the way mine is. You can see the TV face on from some pieces of furniture, and the fireplace face on from others, but all can see the TV and fireplace. I use my fireplace daily in the winter so don't want a TV over it, it gets too hot up there. I would advice against a sectional. You can get the utility of a sectional from a couch and a lounge chair or two. I'd be more apt to angle the couch where the chairs are in your picture. A floor drawing would probably help with furniture placement. I think you could totally redo the room to match your inspiration picture, keeping the wall color unless you really want a dramatic change. I love the curtains in the inspiration photo! Your house is open concept like mine. Hard to figure out whether to repaint or not, because once you start with one room, it snowballs to how that affects the other rooms. You could always do one wall another color like the current owners have in the photo. Wish I knew what that color was in your inspiration photo. Browns and tans are the worst for me as far as choosing the right one. I burned up a lot of cash in sample paints when I moved into my new house. But it is the right time to repaint, before you move all the furniture in . . .

Welcome to California! Is the wall beside the fireplace large enough to house the tv. I see in one pic attached they have a console table to the left of the FP, i would put your tv there, a sectional would be a bad idea here but you might get away with a sofa that has a chase at the end which would be placed to the side of the sliding glass door.

Something like this.... Furniture focused on the fireplace not on the walls. Float sofa and chairs. There are several ways to place the furniture without having it against the walls.

If it was just my husband and I it would be fine the way it is. with children it’s a huge safety issue because if they stand on the couch they can go down the stairs. It’s driving me crazy to say the least. I feel others might look at the room differently than I would and would have a better idea