My dad (79) sees my mother as two different people now. He is paranoid that the other person is stealing. Anybody deal with this?

-79 yr old father (Andy).
-His mother (Rose) had the same dementia, paranoid
-My Father (Andy) has terrible anxiety
He recognizes me and my sister and father's (Andy) memory is probably at 50% of what it used to be, never had an issue with recognizing me or my sister, it is only his wife (Carol)/ my mom that he talks to her sometimes as if she is a stranger, "Where did Carol go?".
He (Andy) still laughs, can make jokes, watches his grand-daughters play sports on the internet, but it is his wife (Carol) that he sees as two different people and because of covid, they really haven't left the house in a year.
Has anybody experienced this with a parent and any advice on how to deal with him seeing his wife as two different people?