Hi Roberta & welcome to the board.
You may want to consider having the guests sign fabric blocks, rather than a finished quilt. Iron the blocks onto freezer paper to stabilize them and make them easier for writing. Draw the seam allowance and provide appropriate pens.
You can do a google search or search on this board for "signature quilts" as memory quilts are sometimes (but not always) associated with clothing from a loved one who has passed.
Here's one with lots of good ideas:
http://www.quiltingboard.com/main-f1...s-t209902.html