Several months ago Martha Pullen spoke about how she cleans those antique clothes she collects. It involved having a bucket that she let them soak in and if I remember correctly she used Biz. As many colors as there seem to be, you will need to consider that some might "run" and separate them. Before sewing together I would soak them to remove the stains and then gently rinse until the water is clear. Then using either either spray starch or sizing I would press them. Remember that the spray starch would need to be washed out after the quilt is finished because moths like starch.