Please do not beat yourself up because you can not be there for the daily care. Hospice is a wonderful option for those who are able to use it in a time of need. Please know that under hospice care your mother will be getting a lot of assistance...not only with his medical, hygeine, daily care...but also spiritual and mental care. Most hospices have on staff clergy and therapists at your disposal and if I were you I would recommend to her that she take full advantage. But for you too. I do not know where you live but many hospices offer counseling services to people like you...family of the terminally ill. When going through hospice with my grandfather...I can not say enough good things about our experience. Our local hospice even has a summer camp each year for children who have suffered through the loss of a loved one the past year.
The best to make yourself not feel so down, is to talk to both your mother and brother as much as you can. I am sure you all know of eachothers' love for one another...and you must know that your brother is aware that you would be there if you could.