@Abbe54 You can create a master listing for all 4 units at once. But you then have to create a listing for units A,B,C together, units A and B together, Units C and D together -- you see the problem? So many combinations to stay on top of.
How many of your guests have expressed an interest in having two or more units at the same time? Would you possibly be creating an issue if you have an extended family renting multiple units for a reunion/event and creating a disturbance for the guests in the left-over unit?