Well they are serged right? Do you have a serger to close them with after you've put the elastic back in? If not do you plan to turn in the edges and topstitch?
As far as putting in the elastic I'd get the right width of stretch Rite knitted elastic and then tack down the top to exactly where it starts on the top of the leg. Then I'd put my 3 step zig zag on and use the longest stitch setting. I'd pull the elastic as tight as I could as I sewed it down and I'd only sew it to the outer layer because sewing it through all the diapers layers is too complicated in my experience for someone who hasn't made a number of diapers.
Again, let me know about closing it.
If you need help I can do it for you and help you with shipping if you need it.
As far as putting in the elastic I'd get the right width of stretch Rite knitted elastic and then tack down the top to exactly where it starts on the top of the leg. Then I'd put my 3 step zig zag on and use the longest stitch setting. I'd pull the elastic as tight as I could as I sewed it down and I'd only sew it to the outer layer because sewing it through all the diapers layers is too complicated in my experience for someone who hasn't made a number of diapers.
Again, let me know about closing it.

