I take it you're not on the
DDP plan so they are able to be on the reservation? I wasn't able to put my BIL on ours when he comes up for two nights b/c we have the DDP. I already told him he won't even have room keys and will have to take an extra one of ours for the weekend since he isn't "technically" even there. But if your BIL is on the reservation then he would have his own cards and I assume he would be able to put his credit card on his keys. But you know what assuming does........................