Hey Monkey,
That sucks. Been through a lot of this myself. It's strange to me, but the least functional kid always seems to end up with the lion's share of the attention, finances, love and support. I left home right after I graduated high school, put myself and my wife through college, and feel good about the fact that I've never needed nor taken help from either of our families. So, feel good about that first. That's something no one can ever take away from you.
The other thing you have to realize, is that every dollar you send to your brothers or your mom, is being used to support their addictions and bad choices. That's hard to hear but you probably already know this. If you give your brother some groceries to feed his family, that's money he can spend on getting hammered for a weekend.
This was an especially tough lesson for my wife and I to learn. Her sister has a son who is a heroin addict. She would give him money every few days which went straight into his arm. He always had some kind of story about owing money to dangerous people, or needing money because he was hungry, or how cold it was and couldn't she wire him some money for a hotel room for the night? Then, when the first of the month came and she couldn't pay her rent, she would ask my wife for rent money. Gut check time.
You can offer to be there for her emotionally, but you have to make clear that they have to live with the consequences of their own choices. Don't help people more than they're willing to help themselves.