May I make two suggestions. Firstly divide the situation in two. One is your feelings and attitude to your DIL, and the other is the situation with your grandchildren. Regarding the grandchildren, it is sad you can do little at the moment, but could you start at least a folder for each of them. In it you could put the birthday cards you are not allowed to send to them, with a little letter saying what you are doing on that day yourselves, and how you are thinking of them and wondering what they are doing. You could also add a photo of yourselves on their birthdays to sort of show them you being with them in spirit. Add any photos of any changes you are making, so if you change your car, or do something different in the garden, put that in with the date on the back.
If you can afford it also perhaps you might have a saving account for each child, but NOT in their name so that you know it is for them but whilst things are as they are she cannot touch it or manipulate her children later on. Then you could add amounts on birthdays christmas etc etc. Hopefully things might change before then, but if you are not allowed to be in touch with them before they are old enough to choose for themselves, then later when you are able at last to meet up, you will be able to give them the folders. They will have that concrete evidence of your always thinking of them and caring for them, however things have been. I wouldnt mention the savings account in the beginning of your meeting up, as firstly they need to know much more of your loving care than see it as a way to get money. Secondly you might then be able to help them if they go to college or need a car or something important in their life. Just to cover that I would also add a letter to your son, to go with your will to explain exactly what those accounts are meant for. As the situation is now, it might not be safe to tell him now as she might wheedle the information out of him.
Then regarding your dil. Firstly I would go for making a loaf of bread!! It is a winner two ways. You end up with a lovely home made loaf which is much improved by the kneading and punching that you gave it thinking of her at the time. When I feel very angry and upset at things that I cant control , I find it a great way to relieve the feelings. If that is not possible I think finding a plump cushion or pillow and do a fair bit of punching it to think just what you would like to do to her. Of course you are not hurting anyone doing that and it will be good to relieve the feelings and let a bit of adrenalin get used up. Another great thing is if you can drive somewhere way up on a moor or anywhere well away from people and literally stand up and shout and yell. Call her all the names that you think she deserves. Shout I could kill you, and I hate you , at the top of your voice. Then look round at the lovely scenery and promise yourselves that one day you will be able to go there again with your grandchildren . Then if you have brought your thermos with you sit down serenely and have a drink and let the beauty and calmness of your view cheer you. Remember that that view will be there to give you peace and quiet whenever you need it. I promise you it will help to have that place , in your mind as well as actually.
All my life good and bad, my beloved Swaledale has been my place and when I go there it reminds me I am like a speck of sand or soil there but that I belong and whatever happens it is a place that I can visit in reality and in my mind to soothe and calm and cheer me , and puts life in perspective. I do sincerely hope that things improve much sooner than this and hope that something will happen to make your son take a stand and realize that life as it is isnt worth living. Try to keep in touch with him where possible to keep at least a link open with your grandchildren, but I would say little of what you are doing or your plans for the future as things are. Just hope that something like this may help you. Oh and you could also write a really horrible letter to your dil saying all the things you want to say about her as she is right now. Write one each and read each others and then rip them up to shreds and burn then. Another way to help your feelings if it is only to write BITCH BITCH , across a whole sheet of paper.
Wishing you all the best and do keep coming to GN as you will find a very wide variety of experiences and occasionally unkind messages but in the main, people are very supporting, and you see that there are other people in your own similar situation and sometimes there may be ideas that can help, as I hope this might.