1) Yes, you can.
2) Each room key can have it's own credit card associated with it.
3) Actually, everyone in the room can have their own credit card on the room key.
4) In that case, each room key has its own limit.
Example: ($1,500 per physical room, instead of $500 per physical room)
. . . Mom uses her own VISA credit card ($500)
. . . Dad uses his own MasterCard credit card ($500)
. . . Daughter uses her own VISA debit card ($500)