You have experienced a very difficult life and unfortunately your parents are part of the problem. For the majority of people, parents care for the children but in your case, the opposite is true. You are now faced with the difficult and inappropriate burden of taking care of your parents.
I understand the fact that you feel responsible for caring for your parents but in this specific situation, you may be doing more harm than good. Your mother is addicted to drugs. She is stealing from you to sustain her drug habit. Stealing from friends and family often is part of drug addiction. Mental health professionals, who work with this population, realize the importance of tough love. Tough love involves setting boundaries and learning how to say no. For you this means asking her to leave. Allowing your mother to live in your home essentially equates to supporting her drug addiction. You are enabling her. How? Living in the home provides her some level of stability that allows the drug use to continue. She does not have to work, pay rent, buy groceries, and so forth. She has no responsibilities. You are taking care of her needs. Living in your home also gives her access to items to steal for drug money. Oftentimes, individuals addicted to drugs have no reason to change. Hence they don’t. When there are not enough consequences for their behavior, an individual addicted to drugs often continues to use. I highly doubt that you want to support your mother’s drug addiction but by allowing her to stay, you are sending the message that “it’s okay to use drugs, live in my home and to steal from me.”
To answer your specific question, “is it fair to ask your parents to leave,” the answer is yes. It is not only fair but is the right choice. It may be one of the most difficult choices you ever make but given the current situation, it is necessary. They are not helping you, they are hurting you.
You asked about whether it is petty to be angry with your parents. Your anger is not petty. It is understandable but it is not helpful. It does not provide relief and in fact, it most likely makes you feel more stressed and overwhelmed.
Please try not to be angry with yourself. You are faced with a very challenging situation that most people would have difficulty dealing with. I would highly recommend seeking support from friends or mental health professionals. One idea is to consider seeing a therapist temporarily to help with the difficult challenge of dealing with your parents. Contact your local community mental health center (CMHC) and they may be able to connect you with a therapist. The staff at the CMHC may also help you access health insurance, money for food and clothing, housing support, and other related services. Another idea is to contact Nar-Anon. Nar-Anon provides 12-step support programs for the family members of individuals with drug addiction.
I hope this helps. Please consider writing again and updating me on your situation. I wish you well. Please take care.