You and your wife need to talk to a lawyer and a financial expert and look into the idea of ending the marriage. I am not saying this to be cruel, but I know if it was me with a disease like Parkinson's, I would hate the thought of our nest egg being drained and leaving my wife with nothing down the road, just to pay the nursing home bills for me. The nursing home only taking half of what you have built up would still allow her to have the other half for her future needs, if you separate. Just because you are legally separated, does not mean that you are still not still married, in your heart.
It's a horrible situation you are in, not only are you going to lose your spouse to this horrible disease, but it's also going to drain you dry financially in the process.