Try a layout with the door shifted 100mm or so to right so that wou could fit bath or toilet on left side. Or move further to get shower on left with vanity over stair. Then cut out your elements and see how the work. Vanity can easily be suspended over stair.

Really fresh, gorgeous and great use of limited space. Well done!

depending on the size of the existing vanity it should be possible to have a similar new vanity or a custom unit made to replace the original but a chat with a plumber should be arranged to recommend suitable options and plan a schedule to remove the old and install the new, including any necessary waterproofing or tile repairs..btw careful removal could allow the original sink, taps and even the counter to be saved and recycled into a new vanity that matches the bathroom perfectly with the added option of being able to add different doors or drawers to the cabinet

Thanks for the measurements, there were a few missing that would have made it easier to be more precise, But I'am making suggestions on what I think might fit within the existing floor plan which you are trying to do. the only small extension is to fit the laundry into a shared family bathroom. As there is already a shower and toilet in the current laundry I think it would be wrong to move them as they are close to your new alfresco area for the family to have easy access when you have your get togethers. To try and keep the girls bedrooms a good size and together with the other two bedrooms I suggest working with the fireplace and making the current Bathroom and ensuite but with the ability to share the toilet with the girls during the night. I have added my beloved barn doors to close off the kitchen from the bedrooms and also to be able to leave open during the day for extra light., the planned deck with roof over will make the dining/study/kitchen darker so you might need to consider a sky light. Anyway just a few different ideas trying to work with and around special features cheers