#1. House rules are a right of the owner of the house. Your Aunt is paying for it, not you, so there is no need to gripe about the lack of Disneyfication that you are allowed to display in her house. My father didn't allow me to put posters on the wall and I was allowed only two framed pictures in my room. It was his house, so I had no right to gripe. I understood that at age 6, so I am having a hard time understanding why this is such a foreign concept to you at your age.
As to the no one being allowed to sleep over rule, I can understand that too. Personally, I am not very thrilled when we have house guests. It's always weird to be forced to look somewhat presentable at all times and God forbid that I sleepwalk!

Of course this doesn't even cover the fact that your Grandmother might be spooked by strangers in the house or have a bad night and go running through the house naked. You never know what some old folks might do if they are not in their right minds, so it could be more about your Grandmother's needs than yours and your Aunt obviously has thought of and will continue to put the needs of her mother over your needs, which is extremely fair.
#2. Yes, wishing your grandmother dead is a horrible thing. I find this comment to be truly inexcusable. Even when my Granddaddy was in the VA hospital and half out of his mind, I chose to volunteer my time at the VA, when I was in high school, just to have an excuse to go see him more often. He was one of a kind and during his clearer moments, it was so neat to see where my own father got some of his expressions and sense of humor. I will forever cherish those memories. My grandparents are all dead and gone. I wish that I had had more time with them.
#3. "Yelling at the world" is not always a bad thing, but if you think that your Aunt wouldn't like to hear what you have to say, why do you think that we would feel any less displeased by it?
#4. Sorry if this comes across a little harsh, but really, it's time for you to act more a bit more mature. I have tried to keep my mouth shut about your postings for awhile now, but really, this last update just pushed me over the edge.