What's the best way to tell kids that grandma is dying from cancer. they are 9 and 5.?

Never easy: This is never easy. Here is a recommendation from livestrong. There are many other on-line and written resources. http://www.livestrong.com/article/201246-how-to-tell-a-child-about-the-death-of-a-loved-one/.

Grandma upstairs: There are many ways to introduce the problem of death. I have often recommended a book called grandma upstairs. I also believe honesty is most important. Children usually know something is wrong but often won't voice there fears or concerns. Talk to them and answer any questions honestly.