I am truly sorry for your loss. May his memory be eternal.
I lost my mother on September 18th to a VERY aggressive pancreatic cancer. I understand the pain you are feeling.
My kids are 27 (she didn't have a problem understanding), 13 and 11. They were not with me in California when she died. We told them that, once we learned she had cancer, that she was NOT going to survive. We were making her comfortable. My boys have lost both of their grandmothers and one of their grandfathers (we had two deaths this year, my father in law and my mom).
How to help them? We told them the truth. In all instances, they were sick and the doctors could not help them. They died. They are now with God and looking over us.
At 10, he should understand the concept of death. The 7 year old might not.
They can however, cherish their memories with him. They can keep his memory alive by talking about him and sharing special times that they had with him.
Again, I am truly sorry for your loss. I hope you have safe travels to South Carolina for his funeral.