Scrills, it's smart of you to think of these things ahead of time. Lots of unexpected things happen in life, and it's good to be prepared.
My father had a neighbor who was struggling with her husband's estate. He had assets all over the place and no list. She found uncashed checks in the house -- big ones, some over $50,000. It turned out that he had never re-made his will after they married, so his old will left his estate to some relatives that weren't even alive any more. It was a real nightmare. I hope your father's affairs aren't that bad, but if they are even a tenth as messed up, you will need legal help for sure!
Edited to add: You should see if you can get a power of attorney that can be invoked if your father becomes incapacitated for some reason. This is especially important since he's not married to the woman he's living with -- he needs a family member to be able to help with medical and financial decisions.
Last edited by SuZenGuide; 11-05-2009 at 12:40 PM.