Sorry, but what space are you referring to? A floor plan (even a sketch) with dimensions would be helpful.

If you are short on storage you could put a corner cabinet there like the ones used in kitchens. Otherwise, I's just put in a single 36" vanity and place a storage shelf unit or tall cabinet in that corner.

Are you sure that the toilet meets code for the distance from the tub? How strict they are for a remodel depends on where you live, but a lot of places will require at least 15" on center even on a remodel and it's not clear that you currently have that.

I'd look into putting the toilet against the wall. That is a weird placement. You really only have room for a single sink, as well as room for one person in there at a time. Teen boys are only going to grow, so I don't see much sense in trying to get two in there brushing teeth.

I'd do what mayflowers recommends. My daughter has a space like that next to the toilet and it is wasted space. I think a nice vanity wth one sink would work well. I had 3 sisters and one brother to share a bathroom with growing up and I can't remember any major problems.

Thank you all for great ideas. I think moving the toilet to that space is a good idea, as well as, adding a single vanity instead of a double. It will give us some much needed room. Thanks again!!

Are you going to leave the tub? It seems if you put in a stand alone shower that could be less long than the tub, maybe even a corner shower where that unusable space is and move things around, you might free up space for two sinks. It would be more expensive if you're moving all the plumbing, but it might become more usable for 3 teens. A floor plan would really help to see if there are some other options. There are some good space planners here.

I agree moving the toilet will give you a much better space if it's possible. I find it gross to bathe in a tub so very close to a toilet - especially with 3 teen boys using that toilet! It seems like a pretty small bathroom, so trying to fit a wall-length counter in doesn't seem like the best use of space. Since the tub must be at least 60" long I assume your bathroom is about 60" to 72" long - you could change the layout to have a vanity with plenty of storage and adequate counter space (somewhere between 30" to 48" vanity) and have the toilet on the far side of the vanity (allow adequate space on either side of toilet for ease of cleaning), attach TP holder to the side of the vanity and then use floating wall shelves or an over-toilet cabinet to give them additional storage, then towel hooks or bars go where the toilet is now.