I am in need of advice and comfort. Can someone please answer. Mother died, sister's gone.....?

I am going to try to make this short as possible. I am an 18 year old high school female, soon to be a graduate later on this month. My mother ped away about 8 months ago, she was the only parent in our lives (sister, brother and myself.) She was a single parent the whole, my sister and brother have father, but aren't consistent and I have never met my father at all in my life, so to lose my mother was extremly devestating. :'( Anyway, so my older brother and his girlfriend who are 4-5 years old than me and also my younger sister who is 5 years younger than me chose to stay all together in the house. My sister's dad chose to accompany us for a while until things went sour between him and my older brother. So my sister and her father don't live with us anymore. My brother and his girlfriend recently gave birth to my nephew who is 3 months. Their relationship has a huge reputation for having terrible problems. It's been off and on, mainly because the lack of care my brother seems to have about anything besides himself. :( Well yesterday, they seperated for good and she no longer lives with us. This is because she found a GREAT job for my brother on Craigslist, got an interview, bought him clothes for the actual interview and he was hired about a couple days later. The job paid $2,000/month! Which was great. But, he quit his job after two days because he didn't like the fact that the job paid every 30 days and not every week or every other week. She chose to left because he only looked out for himself knowing we need help with bills, food and everything. Times have become really hard. I am looking for a job, but at the time I get survial soical security benefits from my mother's ping. I help pay a couple of bills and any food we need. Now, that she gone, I'm not sure what to do. My brother has depended on her for everything, but I feel like he going to be bottom feeding off of me... driving him places, pay for this, pay for that, clean (which he doesn't do any of that). I was really close to his girlfriend and also my little nephew and now that they are both gone, the house just isn't a home anymore. I'm starting to slip into depression yet again. I'm stressed about school, now there are more worries at home. Why would he leave me with all of this? He still doesn't seem to care and doesn't even try to stand on his own feet, that's why she left him because she wants him to LEARN to do so... but I see no motivation. We have $11,000 in property taxes and it's impossible for us to pay it all, so the home I have known half of my life will be gone soon :( *sigh*, I just don't know what to do. All my brother does is invite friends over, smoke, drink, play video games. He is 22 years old. It doesn't even seem to phase him that his SON is no longer living with him nor his girlfriend. Our house in no longer a home and it's draining. So many things have gone wrong ever since my mother has ped and I always seem to be caught in the middle. PLEASE HELP!!!!