We have a trip to WDW planned in about a month. We are staying at The Cabins, 2 adults and 2 children, for 10 days. My sister and her daughter are wanting to come out for part of the stay. They already each have 5 day park tickets that they purchased from a third party. Can they stay with us since we have a room that fits that amount of people? If so, is there anything special we need to do?