Have known a few of my friends to have had a similar problem and they were advised by GP to take each step needed as they are needed and that if the older relative becomes rejecting, cantankerous or even violent...they had to understand that it was just a process and not to be hurt by it. They are not the same people...they have changed with deterioration and have lost their rationale for life.
Would perhaps have wanted to go through the experience myself rather than losing my Mum as I did to cancer...very quickly. I guess life just throws things our way and we have to take what comes with a good and forgiving heart.
Hope it all works well for you.
Best wishes, Mike.