I like my first idea best as far as use of space. I know people say not to put toilets on an outside wall. We had one in our last house in Iowa, but we had 2X6 construction. I don't know how high your window is, but I'm guessing the toilet would fit under there. The shower would be 5 feet long or shorter if you want a wider space to get to the toilet. (kind of tight the way I have drawn). You could do a 5 and half foot long shower and do an angled door at the left end to allow room between the shower and toilet. The vanity would be about 7 feet long, unless you do a 60 inch vanity with a linen cabinet at the door. I would reverse entry door swing if you do that.. The second top right could work and you would still have a small closet. The bottom left plan would require waterproofing your front window. Hopefully someone will give you other ideas. The bottom right plan is bigger, but no closet. Each square equals 1 foot.

Keep playing with drawing til something makes sense. I tried to sketch something out, let's see if I can attach it. Did you want to add a tub, or just a bigger shower? If windows can be added to the left wall, it would really add more possibilities! I made the bigger closet skinny so the window light still comes in. This loses the hall closets so it may need more work. I am not a big fan of the hall between the closets, it was my attempt to keep the window. Either of the closets where the master was could be removed to be a sitting area or a desk area. Obviously I am not a professional. I just like looking at and thinking about floor plans. I am sure others will jump in to improve my sketch by criticizing it lol. I left the toilet and one sink in place. I think the shower could use the same drain and it would not be too bad to extend the pipes to make it bigger, and add the second sink. The entry point is a bit crowded but I was having trouble adding a second sink if I made the bathroom door by the closets.

Do you have another bathtub in the house...for bathing kids? Unless you or your spouse enjoy baths...maybe eliminate the tub in the MBA? I am glad I have a linen closet in my MBA. I agree with eliminating the reach-in closets and adding windows. Also think about how you dress; a walk-in closet can hold all the things people used to store in dressers. (You really don't *need* a window in a closet, although Mark gave it one.) I agree with him about losing the (dated) double doors -- and creating an entry, rather than plopping right into the living room. If you'll eat at the kitchen island a lot, consider seating that's not all-in-a-row. It makes conversation difficult.

Guessing the window is there for curb appeal on the front façade. Have you drawn a mock up to see what that would look like? Sky light /solar tubes add TONS of natural light!! Gotta wonder who the architect was and if it would be cheaper to move the closet so the window is part of the room, than mess with outside walls!!