Should we take Mom to the cemetary o help her understand that her parents are long deceased?
Mom is insistant that she go to Missouri to visit her long dead Mom, dad and sister. She has one sister living who is in worse shape than she is. Should we take her to the cemetary? Should we take her to visit her sister in the nursing home? I ususally just go along with her fantasy that my Grandpa and Grandma are alive but don't know how to hand the constant "I must visit them."
Dementia behavior usually has meaning and your mother's desire to visit her parents and sister infers that she misses them and wants to communicate with them. This is a very common issue for older adults especially when their insight becomes more compromised with their progressive loss of memory. Their perception of reality worsens and even if they know they are in their 80's or 90's, they may still believe their parents live. This is the challenge for the family: Should you state the reality that they have passed away or do they maintain their delusion that they are alive and well? There is no right or wrong answer and depends upon what the answer means to the your mom. Like you said, she was content with the previous answer but now wants a different one.
If visiting her sister, who is even worse than she, is viable and might give her comfort, then it can be done. However, you need to then address her quest for your grandparents. Would giving reality now be accepted and tolerated- that is, telling her that they recently passed away and then taking her to the cemetary to say goodbye? Would she then forget it? Does she have enough retained capacity to grieve or will this 'news' throw her into a depression? These are the questions you need to ask yourself.
Often families will address this quest for lost family through pictures and stories. Since we feel she wants to communicate with them, giving her pictures to talk to, to feel close to, can sometimes redirect her from her desire to 'visit' them. Writing letters to loved ones who have passed away is another strategy that can help; you may need to write the answer too if appropriate.
It does not usually pay to try to convince someone with Alzehimer's that a loved one has died because the issue will resurface due to the memory loss. Instead use the behavior you see, her desire to see them, to help her resolve feelings of loss, abandonment and sadness.