I have experienced this recently. Booked a Ressie on points rented and purchased add on days. Although in the "perfect world" they would always let you stay in the room, it is based on availability. I jumped through hoops as a DVC member to get my 2 ressies hooked at OKW, only to arrive and find they could not do it due to capacity, blah, blah. This used to be much easier in the past then my last 2 rent/use my own points/cash ressies. It seems more difficult as of late.
We ended up being upgraded if you can believe that (1st time ever using DVC...but my HH Cat 1 Bed was not avail due to construction) so we could stay and not move rooms.
When you check in, the 2 reservations should be brought to their attention. Before being physically on property, they will not discuss with the "renter". Good luck but don't be disappointed if you have to move, it is the price you may pay to have 2 ressies. I have also moved. The pain is the moving and the long block of time without access to a room between checkout and check in but any day at Disney is better than being at home.