Do elderly parents use their Alzheimer's Disease diagnosis to their advantage?

Family dynamics are an issue for nearly everybody. If the person is in mid-stage or later dementia, it's not likely that they have a lot of control over memory, yet when someone "fresh" - someone that the person with dementia rarely sees - says something, there may be more focus and effort put into understanding the outsider. Maybe with more familiar family members they aren't paying as much attention. That could be what you are seeing.
Control can be an issue in many relationships. However, if the person has a dementia diagnosis, try to give him or her a little extra compassion. It's not easy all the time, I know.
Take care of yourself, too.
Carol