Although people with Alzheimer's often feel confused or dazed, it does not mean he can not provide information that is true. For example, if a person with Alzheimer's disease tells you that your brother is calling and intending to visit home this afternoon.
Naturally if you are in doubt about the truth of the information. However, do not directly accuse or suspect that he is just making it up. The reason, this could have happened right. To confirm the truth, you can request confirmation from the person concerned.
So do not ignore all the things that people with Alzheimer's disease say. Sometimes, it only takes you longer to figure out the truth of the information they are saying.