Eeeeee - 'Is it too much to ask' - please don't ever use that phrase to your dd. I was a model teenager (no drink, no drugs, no sex, no backchat, perfect grades), never had any particular desire to misbehave - EXCEPT when my mother said 'is it too much to ask...' and it made me want to take heroin and set the house on fire just to spite her.
Sorry, got a bit triggered there.
I think it may be you who has given the impression that this is mainly to do with DD and DH - DD ruining her relationship with him, not being caring to him, not putting him first. So that's what's given the sense that the conflict is primarily between them and you're in the middle.
No doubt you're all trying to do your best. I imagine it takes all your strength to get through the day, too, worrying about him and the dcs as well as having your own life to lead. Why all the focus, again on DH and his many sacrifices, when you are surely making a lot of your own?
Clearly there is more to this story than we will be able to understand or that you will be able to explain on this thread.
It does seem that having a family therapist who can mediate between all of you might really help translate your good intentions to one another. Your appeals to dd to be grateful and caring are not effective, her shouting is not getting her what she wants, DH is clearly not coping, DS is undoubtedly affected somewhere, and you're trying to balance everything, which must be exhausting. If you can find some help to ease you all out of this rut and communicate better without so much blame I think it will take a huge burden off your shoulders. I hope it will.
xx