The Royal Rooms are indeed all located in Oak Manor and Parterre Place, which are on the other side of the river from the main buildings and the main bus stop. However there is a convenient footbridge located just between the two buildings, which provides very easy access across to the main ("South") bus depot. See
http://www.portorleans.org/room-requests.php for more details and a map.
Parterre Place may be the most distant of the four mansion buildings, and some of its more remote rooms can be quite a trek to get to anywhere, but the rooms in its northern-most wing are in fact the absolutely best-located of all the Royal Rooms, with some of them just a few yards away from that bridge over to the main building and bus stop.
There are so many possible jokes, and so little time...
Andre