Re: advice for storing and diapering two floors
We don't spend as much time upstairs as we do downstairs, and I didn't roam our house that frequently with twins throughout the first months. But I did keep a large tote bag with diapering supplies upstairs. It was very easy to fling the handles over my shoulder to cart to the laundry room or downstairs to swap out dipes with my main stash.
My LOs spent nights in a pack n play upstairs in our room. their room & main nap location was downstairs. So, my tote bag was also used to replenish the pack-n-plays changing center supplies.
If you have swings & bouncy seats on every floor of your house like I did it would also be easy to keep a square canvas box with handles next to the baby areas throughout your house. They are great at containing all sorts of supplies & easy to move around.