Can you move the hot water heater? (I presume that's the "HW" in the circle). If so, you might be able to move the sinks partly into the low storage space. People need full height to stand in front of the sinks, but the sinks don't, themselves, need to be at full height.

The trough sink is a cool idea for a bathroom used by lots of visiting kids. (Although I'll admit I've never owned one.) I'd want as much storage as possible near the sink: a shelf under the mirror, shelves or drawers under the sink, etc. for all the toothbrushes and other needs. Also, be sure to have lots of hooks for hanging towels; you could get hooks with erasable name plates, or hang mini chalkboards above the hooks, so each guest knows which towel is theirs and where it goes after bathing. I've stayed at plenty of lodging where I wished for more towel hooks, even when I'm sharing a bathroom with just one other person.

Also, this sounds like a fun place for extended family gatherings!

The OP says she does not want a washer and dryer.

The furnace and water heater space is full height . The diagram is mislabeled. Only the smaller space beside them is low height storage.