It seems as though you've done all you possibly can, both physically and mentally in the way you've brought up your children. However, it is so evident that this child (teen) is so vulnerable and her father's death is the catalyst for further pain that she will no doubt go through until she has the self-growth that teenagers just DO NOT HAVE, because cognitively, their brain is not fully developed. It must be heartbreaking to watch, and the feelings of helplessness must weigh you down, but you're a mother - not a magician, not a psychic, not a God. You've gone through so much, more than the next person, and you will get through it, as will your child. Just have faith. And remember, you are an inspiration!

...that the best contraception that anyone could use is to remind the potential parent that one day the cute little baby that they are dreaming of having will one day grow up to be a teenager.

I was a terrible teenager.  If anyone told me I couldn't do something, I'd go out of my way to prove them wrong.  Fortunately, I still had some sense of right and wrong so I didn't end up getting into too much trouble.  It proved beneficial in some ways sometimes, like if someone said I couldn't pass a subject at school, I'd show them wrong.  But, if I was told that I couldn't go out to a party and get rip rolling drunk... I turned being a wild child into an art form.  I went totally off the rails, and there was nothing my parents could have done to stop it.

Teenage friends on mine were from all manner of extremes.  Some, raised with good parents, good homes, and nothing terrible happening to them, would completely loose control for no apparent reason.  Others, from terrible situations, would hold it together and be every parent's dream.  I also noticed that every child was different.  A family could have a dozen teenage children, 11 of them would end up being good as gold, but one would run wild - and there was never any way to tell which one would do it until it happened.

I have come to the conclusion that, although the way you raise your children and the events that happen to and around them do effect them and their view of the world, and ultimately their behaviour; there is no guarantee that they will turn out the way everyone - including their parents - would like or expect them to.  For some reason, no matter how good you are as a parent, you can still end up with a wild child on your hands.  And even the worst parents can end up with one good kid.  It's a weird little phenomenon.

Given what your family has been through, I would not only say that you have done a brilliant job as a parent, but you could not have done any better - no one could have.  In fact most people would have crumbled and fallen completely apart where you have held it together and kept battling on.  Your teenagers going astray is not something that is your fault in any way what-so-ever.  You have done your job the best way anyone in your situation could even dream of.

The fact is that your children are now entering the realm of adulthood, where they are starting to have to make their own decisions, and they are becoming more influenced by people outside of the family unit - people that you don't have any control of - there is nothing you can do about that.  You have taught your children right from wrong.  If they do the wrong thing, it is now their fault, not yours.  They should know better than to get themselves into strife.  You have taught them how to behave appropriately, and if they don't do so and run into problems with their relationships with other people and end up hurting others, that's not your fault either.  Again, you taught them well, they should know better.  You have taught them what to watch out for, how they deserve to be treated by others, and how to deal with difficult situations - if they let others walk all over them, treat them poorly, and don't want to get out of those situations, that's not your fault.  You have taught them what it is like to have a good genuinely caring and responsible mother - if they would rather live in a situation that is out of control and outright feral, that is their choice.  They know that you are there for them if ever they need you, you have proven that to them over and over again.  They also know how to behave and how they are to treat you in your own home, if they don't, they will loose - and rightly so.  Why you blame yourself - I can only guess that you are having a lot of trouble letting go of the responsibility of being a parent.  There comes a time when you have to let them be their own person.  Your children are starting to reach those times, although at different ages, they each have a need to find themselves and their place in the world, and it's not something you can do for them.

Your older ones are cutting the apron strings and starting to live their own lives and find their own way - and they will make mistakes and get themselves into all manner of strife, but don't blame yourself, it's part of growing up.  Your younger ones, although they aren't totally cutting apron strings and entering adulthood in the same way, they need to figure out where they fit in the world, where they are from, how the other side of their family fits into their lives and they fit in there, and after they stumble around for a while and again, make a lot of mistakes and get themselves into strife, they will then start figuring out what to make of it all as they hit the point where your older ones are now.

And the whole time, they will do what they have always done - but now they are just a little bit better at it and so it hurts more - and they will test your boundaries.  How much will you really put up with?  Can they come into your home after moving out for a while and get away with not treating you the same way they did before?  Does getting older and becoming more independant change the way things are between them and their mother?  They won't be thinking these things consciously, but they will be acting out these questions.

You have no reason to blame yourself.  Of course you won't understand why your kids do what they do, because they don't know either.  Ride it out like you have everything else, and one day your kids may wake up to themselves and apologise for being so horrible.  I did.  Whatever you do, don't be like my grandmother and try to send your children to bed at 9pm when they are 38 years of age and staying over for the weekend!