Accepting people and their ways

Dear Ms. Palme,

How do you understand where people come from, and accept that you cannot change them no matter what?

The reason I'd like your advice on this is because I'm having a lot of trouble understanding my grandparents' attitude towards life in general. I'm 18, and my mom and I live across the alley from Gram and Papa. Their negativity is literally killing us. We love them so much, but we're being dragged down by their constant criticism. Mom tells me stories from when she was younger ~ they've always been the way they are. Lately though, it's getting so hard for Mom and I to be happy and stay positive after we're with them. They are impossible to please, no matter how hard we try. I really, really want to let go of all this and just tell myself they are the way they are. But I can't put up with their critical words and negative attitudes, and the effect they're having on Mom and I. Here are some examples...

- Gram downplays everything (even the death of our dog) by saying "it could be worse. a year from now, we could all be dead."
- Anything and everything will cause them to give us the silent treatment for about a week.
- When we visit with them either over the phone or at their house, the conversation ALWAYS evolves around some tragedy in the newspaper, how their neighbors really aggrevate them by parking in front of their house, how the world is going so stupid and how everything is hopeless and depressing. And then in the next breath, they're telling us to "keep smiling" and even if you're not feeling happy, just smile, "cuz then no one will know."
- In May Papa found out that he has cancer, and after a month of "thinking" he still has done nothing about it and telling him to call the doctor back only makes matters worse.

What should I do? How can I make things happier without trying to change them?
Love,
Maria