I'm not sure making the fireplace look heavier would be a good idea. However rather than fight the off centre I would work with it. Possibly wall hang the TV to the right of the fireplace it looks as if that would make it quite good for viewing from the sofa. Get a bigger rug which would still be off centred but would pull in/integrate the soa area more. I wouldn't put the TV in front of the window as the blockage of the view could feel negative and if the sun shines through during the day difficult to see TV without drawing curtains. What about a mirror above the fireplace you seem to have a window at each end of the space so a mirror could act like a third window reflecting light and giving weight to that are away from the TV. A window seat could work nicely.

Loads of space; loads of options. My ideas for what they're worth: (1) leave Bedroom 1 and bathroom as is. Great arrangement for grandparents/guests/au pair/ teenager/boomerang adult-child. One day you could turn the window in this room into a door for people to have own entry. (2) definitely don't get rid of the second kitchen / wash house extension. Like one person said above, it adds a nice proportion to the back of the house. Just give it some more glazing. French doors are not expensive and would suit well. You and your kids will love all the room on your ground floor when they are older. Compared with houses in other countries (Australia, NZ, USA) what you have is not that big. Families easily enjoy the space you have and can keep up with cleaning etc. (3) get rid of the butler's pantry. It doesn't look a useful shape for pantry storage. It's just a strange corridor. Then open up the wall between the dining room and kitchens, so you'll have a lovely big dual aspect kitchen-dining-lounge arrangement. Such spaces are fantastic with kids. You can keep an eye on so much, be present, and still manage to sit down yourself, or get things done. There are plenty of options for windows at both ends meaning their should be enough light. (4) Existing family room could be a big happy play room/music room/library/hobby room (whatever). Add doors onto the garden. Again, french doors would be nice and inexpensive. There are off-the-shelf products these days for all sorts of doors/windows. Or as one person you could plumb water to this room and make yourself a big boot-room / utility room. Would be great for a family that spends a lot of time in the garden. There are great pictures of these sorts of rooms on Pinterest; most of them seem to be in the US. Some even have a dog shower for muddy dogs, and underfloor heating for the wet pooch to dry on! (5) If you don't have a dedicated utility room, a utility cupboard somewhere would work well. i.e. a place for washing machine, condensing tumble dryer, some shelves for cleaning products, a fold down drying rack for bits and bobs, also doubles as somewhere to hang wet shirts, a counter top for sorting clothes. Doors that slide and fold like an accordion are good for these utility spaces. Just add some ventilation, either between the folding door panels, or top and bottom. Depending on where your boiler is located, you might also put that in the utility cupboard.

We used Solaroof panels on the roof, which help control the sun's rays coming in with UV protection - hope that helps!

I think fire regs might mean that your open plan kitchen living space has to have a door to the stairs. I think you also need to add some cupboards as there is not much storage. One of the most important cupboards is to house the washing machine as it’s important to insulate noisy washers from open plan areas.