I went through a similar situation when I was younger, except I was 14. I know how rough it can get, but when you look back in 15 years you will see how this situation has made you stronger than you could have ever imagined.
Life won't be the same as a lot of people you know, because you have to grow up; like right now. A lot of people go through college to party and slack off like they're still in high school. Get in there and bust your ass to get done as fast as possible. Use the stress and fear of failure to keep you driven and to stay with it and let your siblings help if you need an extra shove. You guys are going to need each other.
Your parents are great because they paid off the house. As long as there are no issues with it - you will only have to keep up with property tax and insurance. If she's leaving you money behind, go see a financial advisor (meet with more than one until you find one that you feel comfortable with). Your school (depending if there is a business school) might have some people who would be very helpful. Don't be afraid to ask for help, or to look ignorant. You have to learn sometime, and the sooner you embrace your position, the sooner you will begin growing emotionally and financially.
There's a lot that goes into maintaining a responsible adult life. I highly suggest you get a white erase board and make check lists of everything. Put it somewhere you will see every day. Then you can put a list of your monthly responsibilities so you can check them off when they're done, and know what to expect so you keep your budget in line. If you get a bill in the mail - pay it immediately, check it off the board, and file it (also get a filing cabinet and keep it organized - if you don't know what folder to file something in, make a new folder just for that) Don't create a stack of mail and try to go through it weekly/monthly or anything like that.
Most importantly, know that you will be ok. The world has a long line of people who have gone through the painful loss of their parents. It sucks, but it's not the end. Your siblings and you will make a great team, make sure you guys communicate and compromise well. Try to keep the bigger picture in mind at all times.
I truly wish you the best and share your pain. Feel free to PM me if you want me to go more in depth with anything or if you want advice on anything. I've made my mistakes, and if you can learn from them than I would be happy to share the insight. I have also made my great decisions, so if you need any advice in business I can help with that too (I'm 27 now, have started and sold 2 successful businesses and currently own a restaurant that's doing so well it's almost annoying) and am getting into the real estate game as well.