Here’s the downstairs floorplan showing the awkward triangular shaped rooms. The dining room and kitchen are separated by a doorless doorway / opening and a small step down. The black rectangle is an open fireplace / chimney

I think I would remove the wall between the dining room & lounge and have that as your living dining space as it is already partly open to the kitchen which would make it a more usable space with dining table near the doors perhaps then seating in the lounge area, or set up as a play space if that’s needed for now. I’d keep the living room separate as ‘toy-free’ area to relax in. .

Thanks tamp75. I thought that initially but then the kitchen diner / living area would all be north facing and would still be a really tricky shape for any furniture with 2 fireplaces

Maybe try to rethink the space as ‘interesting’ rather than ‘tricky’! :-) Personally I think rooms that aren’t a boring rectangle offer more opportunities for layout - they just may take longer to figure it out. Is there anyway to block up one fireplace (although I don’t think it necessary) or to increase light through the addition of another window in the dining or lounge area?
I imagine the wall between kitchen & living room is a structural wall, especially with the stairs in close proximity so removing that may add significantly to the cost & complexity of that option.