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So very sorry you have to deal with this right now. You're right: you don't need any more stress than you already have, period. Turning off the phone, or just refusing to take their calls beyond a "I'm really sorry you guys are going through this but it is not MY problem, it is YOUR problem, and I have tests and other stress to deal with so please don't call me for a week" response, is a very good idea. DO NOT allow them to make you their dumping grounds. If you're not able yet to stand up and tell them off, that's okay; it takes time, like RedPiggy said. But for now, I urge you to simply tell them you cannot deal with their stuff and shut it all down. Remove yourself from that equation -- which is something YOU do have full control over!
What do you do when the world is black? And you cannot afford in time or money to simply walk away for a while? Well...yeah, ducking your head and plowing through it can work, but it doesn't ease your stress. Take time to unwind, even if that's only a couple hours here and there. Make yourself incommunicado. Plunge into something you want to do just for the halibut, even if that means doing nothing whatsoever. Remember that no one is allowed to take control of you, ever. Period. Your parents sound very codependent and have designated you the person to whine at. Refuse. Suggest THEY get counselling. "Mom, I care and I'm sorry, but I can't solve this for you and I have enough to deal with as it is. Why don't you go find a professional to help you through this? It's helped me some."
Hugs.
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