TJP, your story is filled with countless demonstrations of your love and dedication to your children. It is clear that you take every possible action and do everything humanly possible to help them find happiness and success. You are not just a good mother; you are a GREAT mother. Your daughter has a mental illness that has been medically diagnosed. You did not create that situation and you have gone to great lengths to help your daughter find happiness and stability in spite of it. It is not your fault that she has been unable to do so; clearly you have done everything in your power, and have called in the professionals to treat her as well. You are not a failure because she has not been able to overcome the effects of this illness. How could you be? You have no control over this, and to expect that you do is to expect that you have superhuman / god-like abilities. You are a person. Don't beat yourself up over something that you can't possibly control.
The same thought process applies to your son. He too suffers from a mental illness. Nothing that you did "caused" this, either. Addiction professionals and researchers cannot say for sure what causes some people to become addicts. There are all sorts of theories. Most accept that genetics play a role, and clearly you do not have the power to alter your son's genetic make-up. Certainly emotional trauma and other challenging life experiences can play a role and the addict may use drugs to escape. But not always. There are plenty of addicts who agree that their lives were great, fine, perfect before they started their drug use - they just loved the high and ended up in addiction. You did not fail in raising your son; it is not YOUR FAULT that he ended up an addict. So many factors play into it, including peers and experiences over which you had no control, as well as genetics. You are not drawing the line of responsibility correctly in your mind - you are taking on TOO much responsibility, blaming yourself for things that you could not possibly have controlled.
As for your sadness over your children's situations - of course you're sad. Any wonderful, loving, devoted mother would be. Prayer is helpful to me when I feel that way. God has plans for your life, and for the lives of your children. They have their own journeys and lessons to learn, just as you do. I know that you pray every day for God to protect them and bless them and help them to a place of happiness and stability. Beyond that, you have to release them to their journeys and trust that all is unfolding just as it should be.
One last thing - are you seeing a therapist to help you deal with the trauma that you are experiencing with your children? It might be helpful to do so.
So sorry that you are having to live with such pain. You and your children are in my prayers.