Hi.
I can empathize with you on this and i understand the kind of
stress that you must be going through.
The end stage of
dementia is extremely taxing, both for the physical health of the sufferer as well as the mental health of the caregivers. We term the latter as caregivers' burden.
In all probabilities, your mother is unable to feel hunger or thirst. However, instituting a timetable for feeding her will certainly be beneficial. Giving frequent feeds in small amounts, ensuring that the feed is nutrient rich according to the general medical condition of her's will be nice. Also ensure the bed sores are taken care of, with the institution of a water bed, frequent change of posture etc. and local wound care.
'Mercy killing' is a very controversial topic and you will have to get in touch with the local authorities to know about the prevalent laws there.
Regarding you and your sister, i would advice a psychiatric consultation so you can take care of yourself as well, for that will benefit you mother indirectly. Some
relaxation techniques might be helpful for you both.
Hope this helps, and hope your mother has a peaceful life.
Regards
Dr A Rao Kavoor