Oh, and as for being of sound mind when signing/creating a will, I think it is just presumed that the person is of sound mind. No one has to prove that they are of sound mind unless the will is contested. They make you sign something saying that you are of sound mind, but you aren't under any obligation to prove you are. As long as you seem aware that you are indeed creating a valid will, usually everything's on the up and up.
This kind of thing can be contested but it's hard to prove one way or the other if someone was actually of sound mind when a will was written unless it's very obvious that they were not at that time. For example, you can have a serious illness but still be of sound mind, or that same illness that doesn't affect one person's mental capacity could affect another's. Like a stroke, for example.
I think one way to avoid a lot of hassle on this subject is to have the will videotaped. That way, if being of sound mind is contested, the tape can be used in court to determine whether or not the devisee seemed really out of it or pretty put together. Who knows if Aaron Spelling did that. I'm guessing his will wasn't contested by anyone? Anyone know?