There are ramifications to not having a room key, which is also your resort ID.
Persons without a resort ID will not be able to access EMH at the parks, and persons not on the reservation will not be able to board the DME bus. So, right there you lose two of the major benefits of staying on property. And yes, they do check everyone's ID, even kids.
Depending on the resort, you may also run into trouble at the pool. If you're staying at BCV, one member of your party won't be able to use SAB. VWL does random resort ID checks at their pool, and I've heard that BWV does as well.
Really, it's not worth the hassle and loss of privileges. Also, five in a studio would be very uncomfortably cramped. There's very little room to spare once the sofabed is opened, so your fifth person would be sleeping in front of the bathroom door.