First, ensure that both reservations are for the same room type. If one reservation is for a base room and the other is a 2-bedroom suite (which Endless Summer has a bunch of), then it is unlikely you can stay in the same room.
Second, most hotel chain reservation agents have the ability to merge separate reservations into a single reservation. I've done it with both Hilton and Marriott reservations in the past. While I've not attempted it at a Loews hotel, there is probably a good chance their phone agents can do something similar. So call and ask them to merge your reservations together so you can have a single room.
Third, if a phone agent can't merge the reservations, you can try calling the hotel directly, they have more control over a reservation at their hotel than a general Loews Hotel phone agent will have. Hopefully they will be able to merge the reservations. At the very least they can put a note in the reservation to keep you in the same room.
Fourth, if all else fails, when you check in notify the check-in agent of both reservations. In most cases they won't have any problems ensuring you stay in the same room (assuming both reservations are for the same room type of course.) Note that it is usually in the hotel's self interest to keep you in the same room. You won't have to take up a front desk agent's time, they won't have to do an extra full room cleaning (which is more extensive between guests in a room than while the same guest is in a room),etc. So they would prefer not to force you to change rooms either.