Doing this was giving me all kinds of trouble until I decided to bite the bullet and release the elastic for 20" or so at the top and bottom. When I wasn't fighting with elastic it went fairly quickly. I took a good 10" out of the width of the sheets. The pockets are still too deep, but I'm just going to tuck the extra under the mattresses when I make the beds. I won't get to the top sheets before we leave, but I can work with the extra when it doesn't have elastic stretched around the edges! And once I cut out all the extra material, sewing the elastic back in place on each end was a snap.
The length could be adjusted a bit also, but that doesn't have to happen before this camping trip. The weather is going to be in the mid to high 80's, so two quilts apiece will probably be plenty. We may find that we sleep on top of most of the bedding, as it isn't supposed to get very cold at night. We won't be much above sea level this time, and that makes a big difference.
I'm really looking forward to this time with the kids and grandkids!