First investment property - duplex with existing owner occupant

[Chip Clark]

I am looking at my first investment property for a buy and hold rental. It is a duplex with the current owner as the occupant and their son as the tenant of the other unit. The parents are moving out. The son would like to stay. I don't know if there is any contract existing with him since he was a relative, but will find that out before we make an offer. What do I need to watch out for with this special circumstance? Any words of wisdom since this isn't the most common situation?