Can you switch the closet and the bathroom around? That would allow for a window above the tub.

It seems as though bedroom 2 has access to a second, huge walk-in closet. If so, I'd personally get rid of the smaller walk-in behind the jack and jill... then I would get rid of the jack and jill bath and put a bathroom in for each bedroom.

yes, they will use it at the same time if they both are teens and have to get a bus at the same time and no one wants to get up early to be first. hours of shrieking were solved by doing a similar bathroom for our 2 years apart son and daughter. one could shower while the other did 'stuff' at the sink. if they needed to use a toilet while the other was showering they'd run downstairs to the powder room, or use our master bath toilet.

but i'd skip the jack and jill aspect. put the door from the hall, have sinks to the side, straight ahead to the tub/toilet.

or do a single sink, centered in a double vanity, that way they'd each have their own storage area on 'their' side of the sink.

ok, some unasked for parenting advice: when your kids are sick in the middle of the night, you'll want to know it. and when your kids are older you'll like that they come out of their rooms once in a while, even to just use the bathroom. it keeps the number of unsuspected/unauthorized guests down, too.

(been there! my kids are 30 and 32 now and off my plate.)

J&J bathrooms with kids are a PITA the fights begin when they forget to lock the door and they never end . No they do not use the bathroom together nicely if I was building a new house i would go 2 bathrooms or at least not J&J

ok, so this is a temporary problem.... its good to consider at what age they'll move... if its before they accumulate more than bath toys, this might be a problem that doesnt need to be solved. when they want/crave more space, they can move 'up'. yes no?

If you are concerned about privacy, have the only entrance to the bathroom from the hallway.

I love Jack and Jill bathrooms, we have one now and had one in our previous home as well (with the exact layout that you mentioned). I cannot tell what is to the left on the layout. What if you had the large closet open from the hallway? Then you could put in a walk in where the large closet door is now. I think it would be more functional than walking through a room. You could then take out the walk in by the bathroom and make the bathroom bigger or push the bathroom back to the window and give another daughter more storage space. The bathroom is functional as it is now but I would think the doors need to open into the rooms. With them opening in you are blocking the shower/toilet entrance. Also I would add a door to the toilet/shower area or pocket door and a window in the shower. Bedroom #3, I would get rid of the double closet and just make it one big closet with double doors.

I don't really think you have enough room to add a wall to separate the toilet and shower off... Your walk-in closet is already as small as it can be... you could do a 4 foot reach in closet and center the door on the 4' portion. and use that extra space to put a wall with a door in the bathroom. But, you will have trouble with door swings interfering with each other.