Michelle and Max Turnbull are not planning on a happy holiday. Their marriage is in shambles and the D word has entered their vocabulary. But now their youngest daughter, Julia, wants everyone to come to her new house in Idaho for Christmas, and she’s got the guest room all ready for Mom and Dad. Oh, joy.   Their other two daughters are driving up from California. Audrey from L.A., picking up Shyla in San Francisco and hoping to meet a sexy rancher for Audrey along the way. What they don’t plan on is getting stranded on a ranch when the car breaks down.   The ones with the shortest drive are Grandma and Grandpa Turnbull (Hazel and Warren). They only have to come from Medford, Oregon. It’s still a bit of a trek and Hazel doesn’t like the idea of driving all that way in snow, but Warren knows they’ll have no problem. They have a reliable car for driving in the snow—and snow tires and chains if they need them. They’ll