Heartbroken

My grandmother has decided to go back to her house and stay there. There is nothing I can do. We went today to see her. I had been very concerned about her all week. She just sounded awful on the phone but she is so strong and independent. Today was a real scare. She has lost so much weight in such a short time, she can't be more than 100lbs now. The later part of this week she was at home all by herself. Which is my biggest worry right now. Today I wouldn't leave till someone came to be with her. My grandmothers niece, my second cousin, came to stay the night with her. My aunt is going to go tomorrow and stay with her for a while. She demands to stay home. Which I don't really blame her. Who wouldn't want to just stay home in there last days. Especially at the beautiful ocean. But she would be so much closer to most all of her family up here. I just worry about her there all by herself. I am going to do everything in my power to beg all family to just take turns and we can make sure someone is there at all times. I just can't bear the thought of her by herself anymore. Not after what I saw today. This fucking cancer is progressing so quickly now(sorry for the language). It's not the death that I am hurting from. It's what she is going through until then. So much pain, complications and just the stress.

Yesterday my 3 year old asked me if mema(his name for my grandma) is dying? I didn't know what to say. I avoided the question for now. He must have overheard me at some point. Now I am definitely watching what I say around the kids. Not that I haven't been, but now I am being really really careful. Now I am trying to think of how to explain this all to him especially but really both of my kids. How do you explain death and cancer to a 3(4 next month) and 2 year old. My children are extremely intelligent. They are quite close with her and they get that she is sick. Soon I am afraid I am going to have to explain the death part. I am lost at what to say. We are a christian home and believe in heaven but I have never explained any of that to my children. How do you go about explaining death to preschoolers?