Two common strategies that are recommended to work with dementia are validation and redirection. An example of validation is when your Dad is waiting for your mom. You could start with validating that he is missing his wife, and ask him to tell you some things he likes about her. If you can get him to start talking about her, he might start reminiscing about happier times which might comfort him and take his mind off of waiting for her. By honoring his feelings, you’re neither agreeing nor disagreeing with the idea that his wife is still alive.
Redirection is also a helpful approach to these situations. Redirection involves diverting your dad’s attention to something pleasant. Find activities and hobbies he likes to do, a favorite drink or snack, or music he likes, and offer your dad these comfortable things (and educate staff on these things as well) to redirect your dad when he is feeling confused and lonely.
Although lying isn’t recommended as a regular approach, sometimes validation and redirection do not work. If your father insists on waiting for his wife, and you find he is calmer when you tell him “okay”, this approach may make some sense since it makes him feel more at peace.