any dinning plan has to be added 5 days prior to arival at a dvc property,due to differnt computer systems so has to be put in the system manualy.
If staying at any outher disney property it has to be added 3 days prior to checkin
As for geting the QSDDP i carn1t see why not as you should be able to get both the regular
ddp and the DxDDP.someone will comferm or just contact meber services
Any tickets or plans would be added to room key but the plan is per room not per person,so at a meal only one key required to pay or you can all eat seperately at differnt places with your own keys
Paulh