morethan I am so deeply sorry to hear that your DDiL is now reaching the end of her long journey. I'm not a regular kitchener, but couldn't click away from this. What a desperately sad situation for all of you, made more difficult to bear with her husband and mother not being able to agree on her treatment. It must be so hard for you, being in the middle of this and witnessing the distress all round, especially for your poor grandchildren. Her mother just can't bear to accept that she's dying, and wants to hold onto her at any cost. We are all mothers, and I'm sure we can so understand that desperate urge to keep her here.
I think you were absolutely right to speak to her McMillan nurse, not interfering at all, just trying to help find a resolution. I'm sure she (her nurse) will know how to talk gently to your DiL's mother and help her to let go, she will have had so much experience of these situations.
Please post as much as you need, with no apology - we are all here for you. In my thoughts and prayers, as always.