I did one for my mothers 90th birthday and instead of writing on the blocks, I had people to sign on muslin for the backing. I just feel that in the future there can be bad memories over what happened to and within families.
Also, it gave plenty of space for writing. If you like the idea, then you might do the same for do individual squares for families and piece the back, but again in a light color fabric for the backing. This would sure save a lot of time and frustration getting the blocks back in time for you to finish the quilt which I am told and read is a really huge problem with these type of quilts. I also believe that writing on the front of the quilt gives it limited use.