Hello again ladies, it seems I have a lot to respond to. Where to start....
Boe I'm truly sorry about your experience. Maybe they felt justified in asking your sister to leave, but you shouldn't have been treated so badly because of your sister's behaviour. I'm sorry your stepmother was such a cow to live with and that she affected you so much. But I have to disagree about your comment that you think I would be more lenient towards my own child - what I actually said was that I LOVE my own child in a way that I can't love 'A', but I don't think leniency comes into it.
Having said that, I really do not (and have never) treated 'A' badly. My sniping and moaning is done in private (like on here), but I don't let him know that I am feeling negative towards him. Of course there have been times when I have 'had words' with him over something he has done, like the kind of behaviour that I've mentioned on here already, and I'm sure he has known that I wasn't happy with him. But this is par for the course isn't it??! I really hate confrontation though and I try to leave all the difficult stuff to his father.
It's so hard. I knew 'A' when he was younger and he always liked me and we had a very easy-going relationship. But he has changed (as they do), and I had never lived with him before. He has let dh and I down quite badly in the area of trust - we have put our trust in him a few times now and he has 'conned' us and done some things which have shocked us, because we didn't think he was capable of it. Dh also helped him get a second-hand car because he PROMISED he would get work immediately to help pay for it - well that was a few months ago, there is no sign of a job and all he wants to do is go out and have a good time. DH and I are afraid that he will keep up this behaviour indefinitely and if he point blank refuses to find work, we may end up having to support him financially for the next couple of years, whether he lives here or not. Let me tell you, the stress of these issues are one hell of a romance-killer between you & your husband. Neither of you have the energy to deal with it anymore and it becomes depressing... which is why I'm looking forward to 'the end'.
Sorry this has been long... one last comment about whether I would treat my own child the same way - I may love my own child with all my heart, but there is still certain behaviour I would find hard to tolerate, so I don't think I would allow my own child to get away with those things either. In fact I would feel much more comfortable disciplining my own child than someone else's, because I think it's a lot of the UNSAID things between stepparents & stepchildren that really eats you up inside - mainly because the boundaries aren't the same and and you tend to feel as though you have little control. I really think that the stepfamily is probably one of the hardest situations in the world to live in, whether it be because of the stepchild or the stepparent, or both.
Aloha, perhaps if your SD turns into the kind of teenager that tallulah has described and comes to live with you for a few years, you may have some inkling of what I'm talking about. It IS much harder when they're not your own because essentially you are just not related to this person!! No one can deny that there is a definite difference between a biologically-related family and a stepfamily. I think in most cases it's just 'wishful thinking' that a stepparent will come to love someone else's child as much as their own.