A pony wall will actually not give any real privacy to someone sitting on the toilet. Only a separate small room/enclosure would give privacy, and I prefer not to have a separate space with a door because the user will need to wash hands after using the toilet without touching a door knob. Maybe a separate water closet with a two-way swinging door (no hands needed) could work. It’s easier to just lock the door for privacy. Be sure there is a good exhaust fan above the toilet.
On the long sink wall, a tall storage piece for extra towels and supplies could go in the middle of the wall or adjacent to the toilet. Each person will need a bank of four drawers next to their own sink for their personal things. Basic sink cabinets for the bathroom will be 24” wide, drawer units 12” or 15” wide, and a storage tower 18”-24” wide. Each person may want their own mirrored medicine cabinet. If two people are doing their grooming at the same time, a person with elbows out to his/her sides needs about 36” (the space of their sink plus their drawer unit). You may consider recessed mirrored medicine cabinets in a fully mirrored wall over the sink and drawer units. No mirror over the toilet.
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Dimensions for vanity
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