Firstly, welcome to TP. Best place to come that will enable you feel normal when dealing with the blasted disease. Nobody will judge you, lots have experienced the same as you and can advise you on what action to take or to try something else. But best of all never feel alone, and it's 24/7 !
Secondly, don't be so hard on yourself! You have done amazingly to get this far, as well as deal with everyday work and normal things for your existence like bill paying food shopping as well as your mums. That's not an easy task I know as most of us are doing the same everyday. Guess what, we are all tired too just like you, it's known as your body and brain telling you to slow down, take your foot of the pedal even just a little, a cut yourself some slack, after all who says you have to be superhuman?
I was taken on my first decent holiday this year by my eldest son for a week, after caring for my elderly parents both with dementia and my youngest son who has anxiety issues. The holiday did us good, but the sad part was it made me realise I too should be living a life like other people, not just taxiing and attending hospital appointments, seeing doctors and getting test results every week of my existence. And that's what it comes down to I was existing not living.
Since then I have tried to convince parents they need more help but they are too stubborn to accept it, even to have a cleaner or mow the lawn. So I now have taken a step back and don't visit them everyday but do phone them everyday. It will take a crisis before anything changes so I'm afraid that's what will happen and there's not a thing I can do to change it, so until then I pace myself and not make myself so available to take them for coffee etc. I'm afraid I have learnt you have to be selfish sometimes with this disease as you will end up a victim of its nature, and will suck the life out of you literally.
I also know how hard it is to see the physical and mental decline of your loved one, and how infuriating it is when brothers seem to be unavailable when they want to be. I just know that at the end I know my conscience is clear and I tried my best which is all you can do. Try grabbing little things for yourself, a walk round the park, a cup of tea in the garden on a nice day, or treat yourself to a glass of wine (bottle even) for the end of a day. But don't think you aren't doing enough you are doing too much! Review the situation, maybe tell TP what you need help with, carers? Time management? GPs? And I'm sure somebody will be able to help. Keep us posted please.