I don't think I could cope with an open plan bathroom, I like wet areas to be totally separate, the steam entering the bedroom would be of concern and I would not want to even think about a toilet. We did not even like the idea of having the ensuite opening directly off the bedroom, instead have the dressing room opening off it with the ensuite opening off that. Having the dressing room between the ensuite and bedroom totally minimises noise. I find it far more convenient to walk from the shower directly to the dressing room to dress without even going into the bedroom.

reluctant to lose the convenience of outside access to a toilet my suggestion sacrifices a little space off the lounge and bedroom to keep the extra toilet and use the original laundry space for a bigger ensuite with separate toilet and double vanities, the new extension makes a more spacious wiw with only standard doorway openings to the new rooms but the ideal outside door for the laundry will depend on the location of the drying area and you may decide that a western door or no outside door (and walk through the verandah?) could both add more counter space to the laundry and, much as i like the gable roof for the extension, it would be interesting to obtain a comparative quote for a simple skillion roof (and raked ceilings for the new laundry and wiw) that may save a lot of extra roof structure that doesn't add anything to the inside of the new rooms or streetscape and could be much cheaper..

I think you should explore the idea of getting a Pod on the deck. its like a mini granny flat / cabana with toilet and small multi purpose room. You might have the space for this. Your layout looks fine as it is, and if you have a covered pergola, a second toilet in a pod will works well there. I am a bit against adding plumbing and moving walls to your house. First its a mess. lots of putting pipes under the flooring, fixing the flooring again, also ceiling and conrice works, and you end up with smaller bed, tighter layout. Too much sacrifice and not too much to gain.

We intend to stay in our master upstairs for sometime and move down when we feel comfortable OR move them both into the guest bedroom which is opposite the new master. We originally had our master suite upstairs with the boys room down stairs, however we think it's safer this way when they are younger. The 1st floor will be their domain, with their own kitchenette, bathroom, study, living and deck... so they will never have to leave home 😉 I think I have drawn up 300 different options 🤦‍♀️ Does your huaband and his Identicial twin have an amazing bond? My Boys are identical and its incredible to watch how intuitive they are.