How do you understand your elderly loved one when they are in advanced stages of Parkinson’s disease and are going through severe mind changes?

As with AD, I'd suggest that you treat him as though he understands what is going on if you are talking about him, but that you consider confusion about where he is to be a factor in disorientation. The main thing is respect and dignity for the elder. Try to sooth him and distract from upsetting things. You may not always know what is upsetting the person, so do your best and don't feel guilty. It's hard to be right all the time.
Carol

Quite likely that your loved one has advanced from PD to PDD, that is Parkinson's Disease with Dementia. With advancing age, over half of PD patients will eventually develop PDD. This is closely related to Lewy Body Dementia. You can visit the Lewy Body Dementia Association's website, lbda.org for a wealth of information and a forum where you can read about other caregivers with similar problems to what you are experiencing. By joining the forum, you can participate by asking questions, etc.
Jim

mom keeps acusing dad of going out with white women? ages 87 & 86 wants to cause harm to him.