Persons with dementia often have hallucinations, become suspicious, and have paranoia. So, some tips for handling this:
Validate their feelings about the situation and then as naturally as possible change the subject to something more pleasant, or change what you are doing—for example, get up and take a walk with them.
If your loved one is making false accusations about the ALF staff, you could tell the staff that you know that they are doing a good job.
Share a little with the staff about your loved one’s life and their personality and interests before they developed dementia.