Hi, no probs. The thing is with upstairs you are governed by the stairs and the drainage. You can't move either without great expense. To gain more room, better bathroom etc, you would have to sacrifice a bedroom on the right of the plan. Is this an option? The simplest solution is just change the bathroom / toilet and add a shower:- If you need further changes for whatever reason, after all 1 bathroom for four bedrooms isn't a lot, then all I can think of is to split the master in to 2 rooms as it has windows front and back. Then remove the bathroom and make it smaller, giving the bedroom top right a little more room. Make that the master with En-suite and use the bedroom bottom right as the family bathroom. The three smaller bedrooms are an ok size so, in theory could work.

Before you embark on a major and expensive overhaul can I just ask if you/your family are using this new lounge area all the time now? Has it taken over from the main living room at the front of the house? It looks great as it is but you could try a quick furniture change that will cost peanuts compared to what you are considering. If you move the dining table into the lounge area ( lengthways) but keep the corner sofa you could view the TV from both the sofa and the dining table. You could then put the blue sofa in the area where you are thinking of putting the banquette seating. The TV could even be moved to this area instead, especially if its not where you settle down for the night you watch TV, but a secondary living space . As I say it depends on how you use and zone the areas but it might be worth a quick shuffle of the exiting furniture to see if it's practical for you.

If you take the 290 unit off the back run and island, I think that would be sufficient? As you've got kids I think a banquette seat would be ideal for family games, homework, crafts etc. Banquettes are around 60cm, table 90cm so that leaves 113cm which I think is more than sufficient both visually and practically as it's the same gap I have behind my kitchen table. Choose chairs that push under and consider the table legs carefully depending on the number of chairs wanted, pedestal tables often work. I would however take the sink off the island and maybe install a prep sink instead so the back run would be DW, sink, bin, induction hob (I'd integrate the oven personally). Is the shower room a must? It seems quite a trek to reach there with the number of doors unless there was a way to extend the 2nd front door forward and create access from the hall there. Also wondering if you'd considered removing the wall between snug and the old kitchen? It may make the area more useable rather than trying to fill the old kitchen

Your post lead to a lot of questions for me. What are the flow problems you are having? It would be a shame to do more work only to find it doesn't solve the problems you have now. Is it the access to the utility room? If so, would it work better to access the utility room from under the staircase instead and block off the dining room access so you can make better use of the space? What do you use your current living room for now? Would building an extension leave it unused?