I echo the concern shown above for your mum and am glad to hear that she is ok.
I am also concerned about you and your well being. Looking after ailing relatives is hard enough as it is and is harder still of you feel that you are not being supported by those from whom you expect (and deserve) support. What people like yourself sometimes don't recognize is that caring for someone is not merely an act of love or a duty that needs to be fulfilled but a full-time job and one that most people juggle with a full and demanding professional life. You have every right to feel stressed and hard done by.
Firstly where you live? (it gets less sinister i promise :D) and what sort of supports and benefits might you be entitled to from your government as a carer (a term used in the UK for people in your situation) I would urge you to look into that unless you have already done so and if you have, then look again! The benefits may be monetary or social and can help with stresses both financial and emotional.
Secondly and this is important. It is OK to feel overwhelmed! It is OK to want a break and spend time on yourself! Most people feel it is a dereliction of duty to want time off from caring but it is an important element of caring for others. Taking time off gives you a chance to rejuvenate and come back better able to cope. This time off can range from day care for your mum, care package with support workers helping at home or even planned and temporary respite care for your mother in a residential/nursing home or even hospital. All of this will give you a chance to recharge and refresh. In the UK where I live this is arranged by the social services (based on your financial situation of course)
Thirdly your mother may be entitled to some sort of allowance and social care as well
Coming to the situation with your family. I agree with the above comment about their avoidance due to inability to deal with your mother's illness. Or they may just be a bunch of arse holes either way so long as they think you have everything under control it is unlikely that they will step forward. Call a family meeting if you have not already done so and talk about sharing of responsibility etc and how much everyone can and how much everyone should contribute. Make rotas or schedules accordingly. Ensure you include your mother so that she does not feel she has no say in her care. Keep a periodical review of the input with regular meetings which are convened atleast 2-3 weeks in advance so that no clashes arise in the diary last minute.
Lastly and most importantly. Severing ties with family is never an easy decision to make and I don't envy you. My only concern is that if you do you may close the door to potential help in future not just with your mum but with yourself and your loved ones. Make sure that looking after your mother does not mean putting your life on hold. I know it is a hard line to take but you have a life to lead too! It is your life and your support systems for YOU that will matter in the long run.
I clearly haven't given you advice about how to deal with your family but hopefully given you food for thought about how the implications of the considerations you mentioned may affect you in the long term.
I sincerely hope everything works out for you.
Best wishes