It sounds like it is NOT an owner occupied rental.  It sounds like the owner lived in one "dwelling unit" and had two other "dwelling units" for rent.

If all units were equal size and value, then the owner's portion is 1/3 and the rentals are 2/3.  But if they are not equal size or value, then you may need to adjust the percentage allocated to each.

Does that help at all?  If not, please post more details about exactly what you are asking about.