If it gets down to the point where connecting rooms are not available, it's pretty much irrelevant whether they WANT to share a bed or not. The point is that they CAN if they have to. The problem the OP has is that a party of four is within the occupancy limits for one room. She just wants to have two people in each room, so that they each have their own bed. If they want to rent two rooms, they will need to ask if they can have two rooms on a single reservation number, because if they are separate reservations they will need an adult registered in each room, and they have two adults and want three rooms.
I don't know the parameters for getting a single reservation number covering two rooms, but I don't know if it's based on preference or need. If they had one adult and enough minors to exceed the occupancy limit on a single room, they might be able to book two rooms as part of a single reservation. Which may be why it's being suggested that she book a room for herself and the four children, and then the room for the second adult at a later time.
And then you've got an above poster saying you can't book this way, a party of one adult and four minors (age 3 or older) would have to book a room with a capacity of five. The OP would have to call WDW and ask what options there are for one adult and four minors. If the resort has rooms for 5, they'd just tell you to book one of those.. which wouldn't help the OP's party, who want 3 rooms.