sugarpuff seek help for yourself. Speak to Age UK, and to your GP, the problems you are going through are obviously damaging your health. Seek help from other members of your family, they are clearly supportive.
Then take a deep breath and try to think about the situation unemotionally. All, well nearly all, of us love our children and grandchildren deeply and want to spare them any harm, but sometimes the best way to do this is to have the courage to step back and do nothing. To do, not what we want to do, but what is in the long-term best interest of our family.
In this case, I think you need to choose to disengage from your DD and DGC. To a large extent this has happened, but I would imagine that when the next crisis strikes they will be back. When that happens, quietly and firmly refuse any help, express no worries or concerns. Enter Just say no and withdraw. By giving help, by expressing your distress to your daughter, by trying to help, you are actually prolonging the agony and helping the family unit survive.
Once your DD has to stand on her own, without your physical, monetary support and emotional involvement, she may reach the tipping point you so desire. There is no guarantee, but it is more likely than not. Then you can step in and without recrimination offer the practical help she will need to establish herself and her children alone and in safety.