Of course, they were all different sizes (ranging from 11" to 12 1/2") and had been backed with quite poor quality calico. First of all, I cut them all to 11 1/2", except for the smallest one (the one in the middle) which I gave a narrow turquoise border to bring it up to size. Then I gave the ones which had been layered up a new backing, and some machine quilting, and layered and machine quilted the ones which needed it. Then I looked up the instructions for quilt-as-you-go. It semed quite straightforward.
And, hey presto, it is straightforward! Navy sashing, and a bit of slip stitching on the back, and I'm ready to join the rows. Not looking forward to using this method for the borders though. I'll let you know how I get on.