The REM software does not try to model VRF systems.  This is very hard to represent in modeling software generally.  In the case of REM, which is a single-zone model, there is no way to capture the distinct behaviour of different zones.  At best, if someone is modeling a whole multifamily building, we recommend the modeler contact the system designer to obtain an overall seasonal efficiency for the VRF system as a whole, so that the building as a whole can be modeled.

Since the ASHP library does not provide the ability to capture the unusual fan consumption of multisplit systems,  you really need to do it in the Space Heating and Space Cooling libraries.  I would take the approach of creating library entries for the combo of equipment associated with each outside compressor.  For the combos with multiple inside units, be sure to enter the combined capacity. 

On the heating side, use the Heat Pump - Auxiliary Inputs section to enter not just the capacity of built-in Electric Backup heaters, but also (using the "Pump Energy" field)  the extra fan power for the 2nd, 3rd, (4th, etc.) inside units included in the combo.  For efficiency, you want the average heating season efficiency for the whole combo.  

On the cooling side, do the analogous thing.  In this case, you have an input available for entering the Fan Power; in this case, use the combined fan power of all the air handlers in the combination, not just the 2nd & 3rd units.