Maybe you can't get a double vanity, but you can get a double sink, for sure. There is the Kohler Brockway. Doesn't it look made for cleaning up a dirty kid? This one is shot with a fisheye lense on the camera, but I believe it is the 4 ft version. I love the drawers that are steps when the kids are young. You can convert them to drawers by turning them upside down and changing the position of the hardware once the kids no longer need them.

Here is one of the Euro sinks. Duravit and some of the Italian manufacturers make them. Search for "trough sink" and you will find them.

Wetstyle.ca makes trough sinks in Canada like the one below.

And we are back to where we started, with my favorite Kohler Brockway. This is the 3 ft version, hung on the wall.

what a fabulous idea! THANK YOU!

I have a similar size bathroom (mine is a bit smaller,,7.5..so about 1/2 ft smaller). I can't fit a double sink, but you could get a larger vanity. This is one bathroom that I like and it has similar layout with what I have

Real question is whether you plan to include a toilet.

A toilet, which I would expect, would make it difficult to include both a tub and a double sink. There are specific code requirements on space in front of a toilet, 24" I think.

There is an article on Houzz you can search for, "Key Measurements For a Bathroom," or similar name, that has illustrations and dimensions needed.

Typical tub is 60" long and 30-34" wide. For a double sink I would want minimum 60"countertop to have some useable surface area. A 60" counter and even 30" wide tub don't mesh well in a T configuration. Even parallel 30" wide tub plus 18" deep vanity plus even 24" walkway exceeds available dimensions.

My advice: do a pocket door to bath if possible, include a toilet, and if there is at least one tub (other than master bath) go with shower and maybe a double sink will fit. If no tub elsewhere then go with tub, and single sink.

Honestly I don't see room for two boys to fit in 5' X 8' bathroom with a tub. Even if they squeeze in now they will quickly outgrow.

oh, honestly, there are whole families who have shared a 5x8 bathroom for decades. a pair of kids or teenagers will make do. try to squeeze in a lot of storage though -- under vanity, in medicine cabinet -- to catch the increasing number of products they will accumulate! hah.

HUGE difference between "sharing" a 5'x8' bathroom (we have 4 adults with a 7' X 7'4" bathroom) and two people SIMULTANEOUSLY USING the same small bathroom. Which appears to be the INTENT else there is no rationale for a double sink.

Link didn't copy for some reason, just a pic.

it's there! "see ideabook" - very helpful!

Here are a couple of sites with layouts that might help you:

None of them show a double vanity, however. I like the photo Printesa posted. If the tub were a shower, you could build that small storage area shown by the tub and gain some really valuable storage space. A linen tower in my last house's master really added storage, and we found it more valuable by far tan a second sink.
small baths Kohler Floor Plans

The Kohler site shows several plans that are not strict rectangles, basically "borrowing" some space from another room. We used a variation on #3 in our new home for the guest bath, and really like it. We flipped the toilet to the left side, and the area is very private-- not visible from the doorway when it's left open during the day. A 44" vanity is what you see when you stand in the door, and to the right, we extended the area and built a walkin shower, no tub. The "extra" space beyond the shower is in a hall, where we built in a small desk and mirror for guests. The guest room to the left of the drawing has two smaller closets, one on each side of the toilet area. It works very well as a guest room/guest bath, though far from the normal square or rectangular bathroom. The cross shape puts all the circulation area in the same space, so the bath feels larger than it really is, about 55 square feet total.

My links didn't load. Let me try that again:

Kohler sample layouts

Small bath layouts

Those sample layouts are exactly what I was looking for!