Take shirts apart and back with a stabilizer. Cut into 2 1/2" strips, sew end to end with diagonal seam like for binding. The start making strip quilts. Since you are going to make so many quilts this might be the easiest and quickest way to do it. I would save out pockets, collars, and anything else that might not fit in strips, then applique a couple on each quilt. If any of the shirts have his name on it, that would make a great applique. Even buttons from the shirts could be added. You wouldn't have to stabilize heavier fabrics like denim or work shirts, but the lighter ones should be stabilized.