for ground floor expansion of the kitchen and dining room it depends if you have enough budget to open up wall (the wall can be load bearing) so it kinda expensive using 'Rolled Steel Joist'

If you can then awesome here a Plan A and Plan B I would suggest

the most realistic option are extention on the ground floor,

Relocate the WC to the left side of the wall so the formal dining room can be pushed back thus creating enough space for large kitchen in the back,

I enjoy viewing my back garden so I always arrange breakfast table near the back window or door leading there, plus it can function like kitchen island,

for utility rather than creating another expansion better making use of the currently large bathroom by only moving the closet position and divide the room you will have a room for stacked / unstacked washer dryer depends on will you need the sink here or not. Creating the utility here makes sense as there is existing waste plumbing from previous closet and the floor underneath also going through renovation for dining/kitchen extention.

Also it easier since everyone can put dirty clothes whenever they take shower so no need to pick up dirty laundry from children bedroom. I advise to install a new window on the right side of utility wall to make it more brighter,

For study room i suggest to divide the bedroom near the balcony into two, as it will make possible for everyone who want to access balcony not needing to pass through someone bedroom and you still have 4 bedroom although this will be smaller or can be used as other function, i also advise to install two window on the new study room to make it brighter.

Plan B is smaller kitchen but this can allow you to create more freezone on the right side of extention if you consider having small informal sitting with floor to ceiling sliding door to the back garden, oh an I advise skylight on this part of ground floor extention .

Plan A

Plan B

This is really cool 👌 Thank you , gives me a lot to think about

Unfortunately, we would not be able to build the extension because it is a ground floor, but there is a lower ground floor , and only that would be allowed to have the extension z.. I wonder if there’s any ideas with the existing floor plan…….