一对夫妻四个孩子，至少需要三个房间，每个房间至少100 sq ft

（1） Every bedroom occupied by one (1) occupant must contain at least 70 square feet and （2）bedrooms occupied by more than one occupant must contain at least 50 square feet per person.

1 person needs 70 sq ft per room.
2 person needs 50 sq ft per person = 100 sq ft per two persons
3 person needs 50 sq ft per person = 150 sq ft per three persons. 

So a couple with four kids needs 

couple's room= at least 100 sq ft
four kids can stay in
one room at least 200 sq ft
or two room at least 100 sq ft per room.
or three room with at least 2x 70 sq ft, and 1 x 100 sq ft 
or four rooms with 4 x 70 sq ft.

你的明白？