How to keep things clean enough?

You seem to very aware of your Grandmother's short comings. Therefore, it should be no problem to keep your hygiene and food utensils completely separate . Use your bacterial wipes on door knobs, handles, and any other place that she might touch. Buy an air purifier for your bedroom and try to breathe as much fresh air as possible. She is elderly and you and your Mother have moved into her space so try to be tolerant and gracious to her.