B2 is roughly 140" x 72 1/8".
B3 is roughly 140" x 110 3/8" (if you count the 34 3/4 x 29 3/4 area for the door).
B2 vanity runs all the way across the room (72 1/8") and is 24"D. The lav is centered around 36".
B3 vanity is 48"W x 22 1/2"D with lav in the center around 24". I believe the center of the drain is around 9 1/2" to 10" from the back wall (I forgot to measure drain front to back for other bathroom).
B2 toilet drain center is about 32" from the east wall and about 74 1/4 from the west wall.
B3 toilet drain center is about 17 1/4" from the east wall and approximately 41 3/4" from the edge of the vanity. No idea why they spaced it like that.
Here is a very rough diagram. I'll have to do a better one later.
Is it legible?
Editing bc I started the reply before I saw some of the posts.
Frodo, thank you! That is a great idea for wrapping the window.
Neal, did you mean horseshoe shaped? I'm trying to picture horse shaped plastic pieces and having a good chuckle.
Since my bro will be coming in on Tuesday, I'll be up in Alexandria so I might convince the mothership to let me pop in to HD to look around. They have riding carts so she can come in and ride around.
I'm fine with digging in to the wall behind the lav in B3 because I was thinking of building a box for a custom recessed medicine cabinet (if it will fit between the studs-- marking the studs when light conditions are better is probably my next task-- I can see where the panels join up and see the nails so it's fairly easy). I used some handy frog tape to hold my measuring tape in place while I measured a few things earlier, but I need more light in that bathroom.
At this point I'm thinking of running the drain and vent for the toilet in B3 in to the wall with the tub's plumbing and running the one from B2 to the wall behind the vanity of B3 (since it seems to be closer to that wall. If the wall panel behind that lav gets ruined, I can put up some 4'W beadboard to cover it. But I think I will need to go look under the house for joist locations. I do know that one of them is directly under the tub overflow-- hence the notched joist for the trap.
I suppose with a worst-case-scenario, I could cut in to the wall behind the toilet in B3 (but the only walls I can cut into in B2 are the ones surrounding the tub or underneath the vanity).