84-Inch Double Vanity Ideas

We could do any of these double vanity layouts with 84 inches of width.

Vanity Option 1 - Traditional approach

The tried-and-true layout for a double vanity.

Sink bases have false drawer fronts.
A roll-out shelf turns the empty cavern beneath each sink into useable store.
His and hers drawer banks in the center.

Here's a drawing of Option 1:

And, here's a 3D rendering:

Vanity Option 2 - With Drawers Under Sink

You asked about putting drawers under the sinks. That is doable.

Top two drawers, and possibly the third drawer of sink bases are u-shaped to accommodate the sink and p-trap.
His and hers drawer banks in the center.

Here's a drawing of Option 2:

And, a 3D rendering:

Vanity Option 3 - Modern Floating Look

This is a modern design where the vanity appears to float. In reality it is resting on the floor. The toe space is extra deep and tall, and the wood toe kick has been replaced with tile matching the floor. This makes for a much more stable installation.

The drawers on both doors are u-shaped to accommodate the sink and p-trap.
A single drawer bank in the middle for a sleek look.

Here's a drawing of Option 3:

And, once again, here's a 3D rendering: