maybe talk to your brother and tell him you would like to spend some time with Dad too. I do understand both sides. I was expected to take care of my mom but I couldn't due to my job. not that she really wanted me there but wanted me to do everything for her.
Your brother is taking this very hard it seems to me. He is wanting to do it all and that is good for him but bad for you. Tell him you are an adult and do know how to do things. His perception is probably a little off right now with the impending death of the last parent. Your mind does funny things to you during times like this. It sounds like it is getting pretty close to the end. be gentle with the brother but do talk to him about how you are feeling as well hon.