No, not a duplex. Two houses on adjoining lots. Both lots titled to LLC.

And no business purpose in either place,  just collecting rent.

I agree with everything posted so far, and will advise him to see a lawyer about undoing this. I'm not looking forward to the conversation where I tell him his former preparer (deceased) has been reporting this all wrong for years. His tax bill will go up and I'm the bad guy. Great start for a new client - ugh!