I have a small master bath and my designer used mirrors for my cabinet doors to open up the space visually. The doors are the same style as those used for my kitchen but the kitchen has wood instead of mirrors except for a few upper cabinets which have clear glass.

It sounded cheesy when she suggested it but the effect is quite subtle and really does lighten up the space.

I don't have great pictures of the space yet as it's not completely finished but this might give you an idea of what I am describing - the mirrors are actually a very subtle antique which picks up the oil rubbed bronze tones of the fixtures.

Not seen is a tall cabinet - the lower portion of which is a built in hamper which is extremely functional for me.

I would do 2 27 wide 3 drawer bases. That way you have some larger drawers for towels or bigger things. Or you could simply do 2 - 27" bases . 2 larger cabinets will have more usable space than 3 smaller ones. Then hang a pretty mirror on the wall . This will work out great for 2 people to get ready.

Best of luck!

How deep will the cabinet be? You could have all drawers on the bottom, then a small countertop surface in the white quartz, then cabinets (a few inches shallower than drawers) above, hutch-style. You could put electrical in one of the hutch cabinets to plug in electric toothbrushes.

We also have a hamper in ours, but I'm not sure how much depth you have.

Here are some HOUZZ photos:

This one is built-in, but this shows what I was saying about having a countertop area. I would put all drawers below instead of the cabinet and no glass.

This one has a laundry tilt-out, but if there is room for laundry in the bedrooms, maybe drawers would be more helpful to you in the bathroom:

This looks nice and functional with the drawers below; it's across from the vanity and by the window like in your bathroom. I would put a countertop and have the top cabinets a little shallower than the drawers, more hutch-style, if you have the depth for that. If you want an extra mirror, but also want the storage, you could put mirrors doors.

Shallow cabinet would work well, with doors rather than drawers where possible. Perhaps, as seen above, drawers on the bottom and door up top...but with only 12-18" of depth, the drawers aren't the most functional unless you make then deep enough to stand products you can recognize from the tops.

May I suggest a shower rather than the bathtub?

For the toilet "cave"...if it's a shared restroom, even something as simple as saloon doors would add a little privacy without enclosing the cave and allow the two girls to use it together.

One solution would be a IKEA Besta storage combination. Inthis example, the combination is about 47 x 16 x 76 inches -- it sits on the floor -- but you could revise the combination to whatever size, depth, and finish (frame and doors) you wanted. --amateur

The sink will determine how these two similar cabinets function. For most tasks you'll use the sink vanity. The other cabinet would most likely be used for hair styling and storage. For the vanity, I'd use a minimum of 28" for the sink base so that the sink can have a little breathing room between it and the wall. With a standard 24" sink base, you have only 4" between the sink edge and the wall. That leaves you 14" for a drawer stack. You'd want a shallow top drawer for small items like make-up and hair brushes.

For the cabinet you'd want larger drawers for towel storage. 15" isn't going to do it. I would eliminate the door cabinet in that vanity unless you have something tall that can't go under the sink. Drawer configuration depends on how you want to use each cabinet for grooming and what you need to store. If you have any use for a make-up counter and stool, you have room for that option as well.