Sounds like they really could use a good therapist to begin to unpick things first, and of course any medication for whatever diagnosis they have. Depending on where you are, that may not be easy financially if they're struggling for money. Worth having a look to see what is available (and within means) if they're willing to engage with some professional help? From what you say, they are already on the radar of local mental health services?
The damage may not be something which can be undone, but there are usually ways to help manage things better. Hope there is something available they can access to begin that process.