did you follow the instructions on the fabric sheets package & rinse your pictures before using them in the quilts to remove any excess ink?
i would use cold water- very little gentle aggitation- a very small amount of mild detergent if you think you need to (like woolite or dreft)
or take to the sink & run water through a picture first to see if it's going to be ok before heading for the washer-
i've printed lots of pictures on fabric & always test-rinse-cure-heat set- rinse-test some more before determining if they will be used in a quilt or in a wallhanging that will not be laundered. there are so many things that effect the outcome. the prepared sheets you buy at joannes do say to rinse them though---if they lived through that step you should be ok---just be gentle-
vinegar isn't going to make a difference for setting the pictures---you printed with ink-not a natural dye. heat setting & curing (and using a good quality permenent ink) is what makes the difference with inks. good luck