Hello Elvibee,
I'm so sorry you find yourself on this board.
We're a little older than your family. My husband was 51, I was 48 and our children were 16,17 and 19 when my husband was diagnosed with brain cancer last year. We moved interstate 18 years ago, and my parents have both died.
My husband had an incurable cancer and it was really important to us to spend as much time as we could together. His family were welcome to visit anytime, but after the initial visit at diagnosis, we asked them to stay independently.
We just needed to do what we needed to do. It was an extremely sad, exhausting stressful time. We had to make the most of everyday in the way we saw fit. He recently died after 13 months.
It's wonderful that you're available to care for the family. Sit back, let your son know you're there to do anything he wants and wait for him, his wife and the children, to call on you. That won't alleviate your stress in any way, but in this case, I believe, your son has the ultimate say. I loved the fact my in laws understood we needed time to ourselves, and despite travelling hundreds of kilometres when they came to visit, accepted the fact we needed our space.
From the perspective of your daughter in law... this is terrible for her and it is understandable that she has chosen to seek support from her parents. Although my parents have died, I enjoyed a visit from my brother earlier this year. This drew comment because it was at a time when my husband had asked his family not to come. My husband explained my brother was there to support me and he could do this in a way my mother in law couldn't.
Please, I hope I'm not sounding too harsh. In my case, I would have been really upset if my in laws - or other family or friends for that matter - arrived at the house uninvited, particularly if we had asked them not to. We needed out time together.
I wish you, your son and his family all the very best.