Seeing as mil and sil are being so non understanding and claiming innocence (yeah right!). All i can suggest is trying to reason with them, say to them if they had somebody round for dinner who had a peanut allergy, wouldn't they go out of their way to make sure that nothing would contain any traces of peanuts ( I know i would), explain that although these certain foods don't cause you an anaphylactic shock ( sorry if spelt wrong!) but they do cause you to feel very ill and you spend a lot of time trying to keep your illness stable and under control, but to eat some of these certain foods puts you back at square one causing you pain and misery. If your sis still insists its in your head tell her you'll be sure to phone her next time you have an attack everytime you visit the bathroom, am sure it wouldn't get too annoying