I would center the rug on the fireplace, sofa facing fireplace with coffee table..

Put the green piece under the arch opening, tall bookcase where the green piece is currently. Get rid of the mirror over the fireplace and replace with framed art. out thetwo armless chairs in the window with a table between Club chair and casual chairs flanking the FP. it's a start.

Do all six people have to sit in chairs and sofa or can the kitchen bar stools be used occasionally?

I get wanting a lot of seating but the light leather chair looks a bit out of place. I'd center all around the fireplace - so nice that you don't have to worry about a TV here - and think about moving the bookcase along. Doesn't seem like it's serving a huge purpose? Or maybe the green piece goes under the arch and the bookcase goes where that is now. Maybe it's my desire for symmetry, but the one bookcase looks odd to me. I'd see what the couch looks like under the window. Then def some art and a few pillows, throws, etc to bring in color and texture. Two complementary large artwork pieces on either side of the fireplace could be cool. Do you def want to keep the pass-thru?

Ahhh. Good info so far. ✅The symmetrical layout around the fireplace is a good try again. ✅The blue chairs are new so we can do more with them and maybe loose the cream chair. ✅More art will come. ✅The green cabinet could work back at the arch and make room for other things, not the shelf as it’s visually heavy and the first thing someone sees when entering the house. ❓mirror & light furnishing ideas to brighten things? It’s a dark collection and walls. ❓what to tie the brown& black leather and fireplace to the joyful blue, green & pops of colour?

The easiest way to lighten it would be to turn on all the lights. Don’t lay out the seating on an angle, center it on the fireplace. You need to balance the brown sofa,Meitner by having it face the fireplace and flanking it with chairs, or seeing if the blue chairs with a side table between them works. Right now you have too many pieces in the room and it looks choppy.

I am not a fan of furniture placed at an angle for no good reason.

Take the Ikea chair & its footstool out of the space.

Replace the mirror with a beautiful piece of art.

And those rooms are usually large with lots of volume and space so the seating 'floats' in the room.

Yes to the floor plan above. Not only turn on your lamps, but add at least two more. For sure, there should be one in each corner. And you could try for some small lamps on the mantel. How about some drapery panels on each side of the large window. They won't cut out much light, but a light fabric will give you more brightness.

Thanks all of you for many encouraging details. Beverly, the photos and layout drawing are especially helpful.
The window light is such a glare that we tend to not have anyone seated directly under it. They appear as black silhouettes.
We may have some white shelving to surround the fireplace. I’ll see if it works …

Beverly nailed it.

I am confused about your 2 comments "The window light is such a glare that we tend to not have anyone seated directly under it. They appear as black silhouettes." I thought this was a north facing window and you need "Anything to brighten it as it is north facing". Add lamps and don't be afraid to turn them on during the day if you need to balance the light in the room. Would sheers over the windows help with this? Your blinds-only might look better with the softening touch of additional fabric.

I would not add white shelving to surround the fireplace. Too busy, especially with the busy pattern on the blue chairs. I agree that the tall shelving unit does not add to the room.

Just art. Mirrors will only reflect light that shines on them, not make a room brighter.

Is a new rug in the budget? Painting?

Do we need to take into account any colours in the "view" into the office from this room?

With beige, brown and blue you already have 3 colours. I wouldn't add green or more "pops" of another colour. https://www.thespruce.com/timeless-color-rule-797859#:~:text=60%25%3A%20The%20main%20color,the%20colors%20in%20a%20room. Is there colour in the kitchen? It might be helpful to see the kitchen, since this is actually one big room.

Do sheers flanked by panels on the window. You can part the sheers if it’s a cloudy day, and pull them together to prevent glare.

Can we see the room with the furniture moved?

Why not try the sofa floating in the room, facing the fireplace, and then have one chair flanking the fireplace, then the two blue chairs to the left of the sofa and the brown leather chair to the right of the sofa. Below are a few other layouts that might be able to work for your room as well:

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