Just read through your threads, greycardi, and see what a difficult situation you've been in. Sorry, my remarks wouldn't apply to you and your mother's case. You are in a hard position now as she may forget your father has died and keep asking for him. I hope you don't have to deal with this eventuality.
I wondered if she had had a capacity assessment as you wrote about earlier? You can always talk privately to her GP - not sure if you are the eldest or whether all children are considered next of kin? I had an arrangement with the GP that I could ask about her or liaise with them about her medication whenever necessary.
I don't know if it may help but, having to think about your mother and look after her may go towards taking your mind off your own grief for a while. I know, because I had to make the funeral arrangements and everything else that was needed, it did keep me busy for a bit. I think it wasn't until after the funeral that the reality hit me.
It must have been terribly difficult trying to look after two ill parents and you still have your mother to worry about. Wishing you strength to deal with the coming days and weeks. I hope you can share the burden with your brothers.