About the bathroom:
I would place the sink on the wall at the bottom of the plan on the right side of the door. Then you also have nice light from the side window.
The shower top left on the plan and the toilet on the bottom left wall of the plan.
About the rest (you didn't ask for it, but I have to get it off my chest anyway):
To be honest, I don't think the design is successful. Such 45-degree walls just so you can somehow get behind the straight staircase :confused:
The dressing room is practically not usable as such.
You have already received the note about the fold-down attic ladder above.
Sleeping and dressing is a huge area that, in my opinion, you cannot use properly like this.
I would straighten the walls and divide the office space between the two children's rooms. That way you can move the hallway wall on the left of the plan further to the right. Put the office where the dressing room is now and set up a proper bedroom on the left side of the plan.