Hi,
I lost my father last year to cancer. This is hard to bear still - nothing and no one can replace a father or even come close. Only thing I can say is keep him happy and pain-free, and spend as much time with him as you can doing happy things. Perhaps he enjoys a card game, or a board game....or would like to read your children a book. As long as the kids are not too jumpy around him, let them spend time with him (would be a good change for him too).
Get some support for yourself - its ok to cry once in a while. Don't think you have to hold it all in for the sake of your husband and mom. You are human too. I hope for your sake that your father defeats the disease and proves all doctors wrong. Take care, and hang in there.
Priya.