I have friends like this too. you know them better than I of course, but I doubt that your friends don't care at all about burdening their parents. imo, guilt is just not a very effective motivator for someone to get their life together. it tends to make them feel bad and get even more set in their ways. the only way I've ever seen this work out is after some spark that gives the person an intrinsic desire to improve their own life (and the belief than they can).

as for what you can do for your friends, there's probably not much. the best you can do is to live well yourself and be a good example for them. also, be careful. there is some truth to the saying, "you become the average of your five best friends." if you get too involved in their day-to-day, you will experience friction when it comes to accomplishing your own goals.