Almost everything is doom and gloom with my mother, why?

My mother is 84 years old she has never been abusive or mean but over the past couple years seems like she complains about everything obsessively like the property line between her and the neighbors or my brother not picking up mail at her house (why he still gets mail there i have no idea hes 55), when my brother visits he only lives 10 min away she looks for things to complain about all doom and gloom with him and when he stays away for more than a couple of days she complains about that saying he dont care about the family and she dont care if he never visits again to the point he hates going to our moms house. if he goes to the grocery store buys extra meat,chicken whatever ,she tells me he buys cheep meat and it makes her and my younger brother sick, when i visit we go to the same store and its the best tasting food shes eaten. my younger brother still lives at home with her hes 50 and the baby but its like there married and beleive me no one i mean no one better say anything at all negative about him she will rip into anyone that does, its like you can see the change in her face and a totally different person comes out like she is posessed. I live 650 miles away but call everyother day talk to her and I have been hearing the same topic for a couple of years complaining about the neighbors ,my older brother,same topic same story every time i call ,but i listen i console and talk it thru as usual and try to sound supportive its not easy after hearing it everyday. Ive had a talk with my brothers and just told them just agree with her and to keep the peace and keep her from being upset because you dont agree with her. i omit im 650 miles away like i said but actually talk to her more than my older brother that lives up there so i do here it as much as them i just dont have to confront the problems directly in front of her. I go back home twice a year for a couple of weeks each time, when i visit my car is full of tools i bring to work on her house fixing things repairing, painting, remodeling, yard work etc my younger brother helps me as much as possible but hes dissable with back problems and cant lift anything but hes always right there with me the whole time doing what he can with me, the older brother he just stops by says hello talks for awhile sees that im working on the house and leaves and says looks good as hes leaving, no problem there I dont think he could change a light bulb without calling a electrician.the biggest problem is i cant seem to get thru to my older brother that he has to watch what he says in front of our mom dont question her she gets confused and angry with him he just says he is tired of her wanting him to look at a property line or bitching about the neighbors my mom crys he goes home and in a few days it starts over again with the same thing. When i come up i try to get her to go out to eat go for a drive try to talk about anything to change what goes on day to day but even if we go to a resturant she brings up the same topics and complains about the food prices. Everything is doom and gloom ive tryed tacticly to talk with my mom saying "well mom we will put a privacy fence up if you want and we will just pretend they dont live there and we can ignore them" she looks up at me and says WHAT DO YOU WANT ME TO DO KISS THERE #@#! I DONT WANT A FENCE! well i havent said anything tacticfully anymore. Like i said shes 84 in good health shes on no medications and walks and gets around as good as a 50 year old she gets her hair done once a week at the beauty shop and seems normal but wow she is obsessed with just complaining and doom and gloom nothing i mean nothing is happy even growing up my brothers and i never herd my parents bickering or fighting but my father died in 1978 of a heart attack untill just recently my younger brother told me she threw all of his pictures in a drawer and is now bitching about she should of divorced him years before he died and says he never treated her right and has been downing there marriage that we thought was always a happy marriage. Its like she is looking for more doom and gloom. whats going on is this normal? .