Sit down with your mom and an excel spreadsheet. Identify all bills that she pays every month and when they are due. You'll need to go ahead and look at doing a power of attorney before she loses the ability to communicate. You also need to have her explain how the bills that are not monthly (home insurance, car insurance, property taxes, etc) usually arrive. Do you get a notice in the mail? An email? Speaking of emails, have her go ahead and give you the password for any email accounts, online billpays, shopping sites (ie amazon or itunes,) if she has digital media you'll be wanting to access. Have her go ahead and add you to any bank accounts. If she has a savings account for your brothers college, now is the time to learn about that. Unfortunately, probate can sometimes take a bit, and you don't want to be out of pocket during that time. Another biggie is to identify any automatic withdrawal payments that might be set up.

If your parents have an attorney they use, go ahead and get in touch with them and see how to lay the appropriate groundwork there. One thing to go ahead and negotiate is fees. Many times they try to work for a percentage of the estate - I wouldn't recommend this. Many times people undervalue the estate and end up paying way more than they should have. Go ahead and negotiate a flat fee or an hourly basis (with time accounting)

Lastly, do NOT drop out of school. If your siblings were young I can understand, but 15 is plenty old enough to take care of themselves after school or even get a job and contribute towards the family. Your siblings need to understand that everything costs money, house, food, utilities, and the more they contribute, the better it will be for everyone.

The biggest thing is this, don't be shy. Your mother knows she's dying. Don't pussyfoot around, you need to ask direct questions and make sure you get a direct answer. Your mother wants you to be successful after she's gone, and I'm sure wants to do everything she can now to ensure that happens.