My goodness you could teach a master class in meddling! You are overly involved in your son’s marriage and I would not be surprised if this was another aspect of the marital discord. You had no business calling your DIL’s mother. You shouldn’t have been discussing anyone’s marriage but your own at all. Decent grans don’t further discord in an already contentious separation. If you love your grandchildren you put your desire to meddle in their parents marital issues far out of your mind. You chose to pick up your phone and cause more drama, an action which I cannot find a single positive spin for. You speak of your DIL’s lack of maturity, yet here you are throwing a tantrum because she won’t do what you want her to do—which she has zero obligations to.
If you truly don’t want to cause more trouble than you already have, redirect all requests to see the grandchildren to their father. The woman is going through a divorce and impending single-motherhood. Leave her to sort her life and you deal with your own son. If the man you raised can’t be bothered to keep his own children connected to his family, that’s a reflection of his own values and character. Your issue is with the one you birthed.
Do stop the drama-mongering. These poor children need stable, loving support through this transition. If your son is failing to ensure you can be a support, at least remove yourself from the middle of the chaos and step back. This isn’t about you.