I am only 15 - so this may not be much help to you but i will try anyway!
My granny, who is 88, came to live with us permanently in a converted granny flat we had on our extension whilst my grandad went to stay with his sons (my grandmother got re-married so he is kind of my step-grandad). She couldn't look after herself and to be completely honest, at the start it caused alot of friction and tension between my family and my parents especially. However, now things have settled and there are many care packages available for her which gives my mum a break. my mum gave up her job for this, and i know she finds it very stressful sometimes and you do need your space (even I need space from my grandmother!).. but then again it might be easier because it is your mum, and not your mother-in-law as it is for my mum. It would also mean you can relax after work a bit more and get home!
Sorry if this is not much help but maybe you can sort of relate to it haha! Good luck with everything, hope it turns out ok xxx