Deb is right, and it COULD get pretty complicated if you aren't within the 11 month booking window for the specific resort you are looking at. It kind of depends on the size unit, time of year, and resort, but if what you are looking for is on shorter notice and during a popular time of year, it could be hard to find that available room from two different owners. THe best would be if you got the two of them in contact with each other and had them set up a conference call so they could make the ressies at the same time through the same MS agent. That way you KNOW your unit is available to add on dates and that the ressies will be linked.