Steep hills and heavy loads points you at the mid-drive bikes like Tern GSD, Momentum PakYak. The Tern uses the Bosch CargoLine motor, specifically developed for cargo bike use. The PakYak uses the well regarded Yamaha.
I know regular users of both those bikes, whose main purpose is carrying two kids to school and nursery, and both kids and rider are blown away by how good the experience is. They have no previous ebike history, their comparison is car, and they prefer the bike.
But they are not cheap. About £4k the PakYak and £5k+ for the GSD.
The third bike type I see round here is the three wheeler with a big front cargo container and hub motor. In most conditions they are no doubt fine, but the image that sticks in my mind is a rider in bottom gear struggling up a short, sharp hill at below walking pace with two kids on board. A speed where the rider is doing most of the work. Not fun on the school run.
If you want to go the potentially much cheaper hub motor route, make sure you fully understand the fully laden performance on your local hills.
And the fourth type is a Shimano mid-drive two wheeler with a smaller front cargo box. Not for kids, haven't seen it in use much, but goes OK as far as I can see.
Money no object, I'd be choosing the Tern, but like all eBikes, there's about 30% in that price I don't want to be paying!
On range, Tern has the Bosch two battery kit already installed, although the second battery is an extra. Pakyak has a lockable storage box which might take a second battery.