If you were to use a narrative report, this assignment could be handled as one report. First you would describe the property in its entirety as it presently exists and provide a value. Then you could break out each parcel and provide separate values. By doing it this way you end up only presenting the basics regarding zoning, HBU, neighborhood/marketing area, flood, environmental, assessment, pictures, expansion potential, etc. information one time rather than two or three.
Doing it like this would also provide your client with an idea of what the whole parcel is worth and what each of the individual parcels are worth, which may impact their decision process. Unless the two parcels and the related improvements are absolute model matches, it is very possible that each parcel will have a different stand-alone value.
When developing your HBU would it be possible to construct additional units on either of the parcels if separated and/or on the parcel as a whole. Could a third duplex or larger building be built along the end of the parking area, creating a "U" shaped situation?