Is the box actually big enough for two people?!
It's big enough for two small people. Before the pandemic I often took Lukas and his buddy together in the box. Sitting on the bench together side-by-side there's still plenty of room for each of their backpacks.
One of the other moms at Lukas' pre-school has a similar bike and has apparently managed to fit both kids and her wife in the box for a short trip. I'm impressed but have not attempted to do the same.
That sounds like quite a workout for the pedaller...!
Well, on her bike, yes! She doesn't have electric pedal assist like I do. :-p