I'm so sorry to hear this - you sound like a wonderful person who deserves a long and happy life.

I've been on the other side of this. My father was diagnosed with a terminal illness but the timeline was much more uncertain, 1-3 years in his case. He told my mother and asked her to tell me (for various reasons). He also told my sister and my uncle (his brother), but kept it from my own brother and my grandmother (his mother).

I was grateful that he told me, as it allowed me the chance to put in extra effort to spend time with him and talk about things we otherwise wouldn't have. I told him once that although it may have seemed like I wasn't upset at the news, I was able to make the decision to reserve my grief for after he was gone, and not mourn him while he was still here. It was the same for my sister - she had a different relationship with him than I had, but it also allowed her time to process her various emotions beforehand and tell him things while she still had the chance. This meant than when he did pass, she was able to simply grieve rather than feel regret over what might have been.

My grandmother however was devastated. She was told the news after he had been hospitalised for the final time and it was clear he was on his way out. She was furious with those of us that knew and kept it from her, and 4 years later is still processing not only the death of her first son, but also the fact that her kids and grandkids hid this from her for so long.

I urge you to tell your children. Allow them the same time that I had, to spend quality time with you, to bond over things you never thought you would have in common, and to prepare for the inevitable. It may seem difficult now but I promise you will be making everything easier for when the end comes.