My aunt has dementia and keeps accusing my family of stealing money from her bank. She yells at us how do we manage this. She is In a retirement home?

Relatively common. In advanced stages of dementia. She may have developed delirium with paranoid features. Would suggest letting her physician or the nursing home staff now as she may become agitated and needing to be medicated. It is otherwise hard for family members to see their relatives turning against them with no reason.
Recommend. evaluation / treatment by a geriatric psychiatrist. Then a comprehenisve treatment plan can be developed.