Wow - I'm very sorry to hear this... it's heartbreaking. The exchange students should be having a wonderful experience instead of this type of negative and guilt-tripping experience. My only suggestion is to treat them yourself as best you can, be a good supportive ear for them and be supportive... go with them places if you can, even if it's just for walks nearby. Try to make up for where your parents are lacking, if and when possible. It's really a shame that your parents are behaving this way, as though it's a burden to them. They never should have agreed to do so. Maybe also give your parents a good slap upside the head and set them straight yourself.