According to the book I mentioned above, 'In Georgian England, much of the gaieties of Christmas seem to revolve around Twelfth Night, the last eve of Christmas..." The Gardiners only stayed a week so it would seem they spent part of the Christmas season with their children; perhaps Christmas day itself was spent at home or maybe their own family celebration was Twelfth Night and they were home in time for that or they may even have spent the week with the Bennets between the two days and were with the children on both Christmas Day itself and Twelfth Night. :)