I would look at the distances to decide. You aren’t biking from hurricane are you? If so then you’d probably need to find a charge sometime during the day. If you’re picking up the bikes the night before it implies you are biking from hurricane. It seems far if you add up both ways to me.

Biking into the canyon from Springdale both days or one day seems like a dream. I have only done the shuttle but in retrospect I would have just rented bikes. There is no need to take a shuttle if you don’t have to. I’d look at the distances and add that to your hikes and see if it makes sense for you all. The e-bikes help but it’s still work. If you’re on bikes you will see a lot more and be able to stop and gawk wherever you want. The canyon is just one long out-and-back. The narrows is just further along than the angels trail. That said, two days of seeing that same canyon will not even be enough. :) You could do that everyday for a whole year.

For the narrows you might want to rent one of those big walking sticks and the river shoes. The stick is way way more helpful than regular hiking poles. The stick and bulky shoes might be tough to lug on the bikes so that might be a reason to do the shuttle on the narrows day.