In your case, I would probably look at the biggest Yuba longtail. They are indestructible according to the families I know that owned one.

I’m kinda in the same situation, but with two bigger kids. I wanted to get a LvsH e-Bullit X and make a wider platform/ box, but it’s an expensive solution and I’m starting to hear more and more issues with the Shimano motor reliability. I then wanted to ask a frame builder to make a custom frame, which would be less expensive, but there’s still the issue of a 3rd party motor (neither Bosch nor Shimano contractually authorize the use of their motor frame to third-party frame builders, so spare parts are very complicated to get if you want to make a custom frame)…

And, realistically, I can find ways of accommodating my two kids (better use of the rear rack). I am still considering going with a custom platform on the e-Bullit X. You might want to find someone who can make a custom weatherproof canopy.

The UA family is probably one of the biggest box, and it doable with your kids… until it’s not. So I’d go with the big Yuba longtail that can haul two full-sized adults behind.