It’s either custom build…….or have you tried going to a lowe’s or home depo cabinet specialist? There’s a lot they can help you figure out. I went there for bathroom cabinets at our last house. They were able fit drawers, spacers and cabinets together to fill the space. Quality can be variable depending on the cabinet manufacturer picked but I would guess they can help with the design.

You will not find a single vanity in those sizes. If you are between 2 walls, then it will be a combination of 3 cabinets and 2 fillers ( similar to how kitchens are done ) .

For the second vanity - 16" deep is a HUGE problem. Even an 18" deep cabinet can be troubling to find a sink and faucet that will work where the sink isn't tiny like an airplane sink! I am surprised that is even the way the bath is designed. That really needs to be reviewed - or post the plan here an we will try to help

Is this a new build or a remodel?

The only way you'd be able to do 16" depth on a bath vanity would be to do wall-mounted faucets and vessel sinks, OR, you could do a long trough sink, OR, you could have integrated sinks made from your counter top material. The latter is an expensive, custom undertaking, but it can be done. See examples:

Minimal Modern Spa Bathroom · More Info

Shelton Bachelor's En-suite · More Info

Cardiff Mid-Century Modern Beach House · More Info