Units #2 & #3 can also be combined by unlocking an inner door between the kitchen of unit #3 and the bedroom of unit #2. The combination of units can sleep 2 couples and 6-8 children depending on their ages.
Units #3 & #4 can be combined by unlocking the door between the two living rooms. Together there are 3 bedrooms and 2 baths. Add to this unit #2 and you have a sprawling estate with 4 bedrooms and 3 living rooms with 3 couches!