Welcome to our little corner of the world. I too have done a lot of research on the subject of Alzheimer's. My mom has it and she is now 84. Fortunately, she has not had delusions such as your dad. I would imagine that must be a very difficult thing to deal with. What about his physician? Could you try to talk to him and see if he can give you some advice or direct you? My mother sees a geriatrician who specializes in memory loss and Alzheimer's. He's been a wonderful resource for us. In addition, he has a social worker on staff that we can set up appointments to meet with her and ask questions.
You might want to try a support group or call a nursing home and speak to the head nurse of the Alzheimer's wing or floor.
My mom lived with me for a year and I found during that time that when she became upset, the best way for me to handle her was to speak to her very calmly and lovingly; it always seemed to calm her down but, then again, she wasn't delusional, well, except for one incident one night when I was taking her to bed. She has to walk up 7 stairs to get to her bedroom and every night she would complain about the walk. This one night, she told me she wasn't going to walk...she was waiting for her "ride". When I asked what it was and where it was, she told me it was in my living room ceiling and all she had to do was call for it and the celing would open up and it would come down and take her upstairs. I was pretty shocked and just said ok mom, then call for it and she did and then told me it wasn't working that night and finally got up and walked upstairs.
I do know from what I've read about Alzheimer's and delusions that the delusions are very real to the person.
You might want to call the Alzheimer's Association or go to their website at www.alz.org. They do have a hotline with 24/7 support. I have called and they were really wonderful. You could also Google "Alzheimer's and delusions" and go through your search. I hope some of this helps you. It certainly is not easy dealing with someone with Alzheimer's. I wish you and your family well,