pre-wash- and toss in a color catcher- or a piece of white fabric- if it comes out with color- rewash- until no more bleeding-
you can use retayne- follow the instructions on the bottle -to help set the dye if you have a bleeder.
you can use synthrapol to keep any fugitive dyes from getting on other fabrics---it keeps the dye in the water instead of on other fabrics- again you must follow the instructions-
but the easiest way is to wash them until they do not bleed-you need to at least test them for color-fastness- but most charities require the quilts to be washed before sending them - always check with your chosen charity before sending in any quilts to make sure they will be accepted- and their requirements.