I'm so sorry for you, my prayers and thought are with you...

My father died of cancer 3 years ago, (doesn't seem that long though), it was a sudden diagnoses and too late for any treatment. I am the baby of the family and they kept it from me for a couple of weeks before I ever knew, they gave him a few weeks to the most 3 months...he finally passed after 6months in a wonderful hospice center...it wasn't easy, and knowing/looming was heartbreaking but I was thankful for it in a way, to have those moments to talk, to share....but it in no way made anything any easier when he did pass.
I know someone else said it, just listen, be there, be the shoulder to cry on, he might even get angry, just try not to take it personally. Try to embrace the time you have with them...

Hugs...my prayers and thoughts are with you.