What are your brothers role in all of this? Do they contribute to your parents as much as you? Do they give half of their salary to them?
I think you need to put your life and well being above pleasing your family. It seems like your being perpetually guilt tripped into supporting your parents. Think of your own future and where YOU want to be in 10 years. Your brothers don't seems concerned with your own life's well being from what you wrote.
That's a really good post and good advice in general.
OP - why does it always have to be you that does all this for your parents? What are your brothers doing all this time?
I think there'll come a time when you'll need to stand up to these brothers of yours and tell them to play their part. You'll have to force them to "understand." (they may not but in the end it won't matter, since they don't seem to be caring too much about your well-being) Put your brothers in their place and tell them to get lost.
It's only when you mentioned your fiance that I remembered who you are. If you want to marry this girl you need to make it a priority. Once you do that and make the break with your family (to some extent) you might start to see things a little differently, especially if/when you have children of your own.
PS I always hated that term too, "man-up" - it's one of the dumbest things anyone can say. Unfortunately a lot of people will use it though - and not just men.