Sounds a right nightmare and whatever you get sorted, there is still something next they find which delays them either further coming! I know it's not easy, but try not to count on certain dates as that will make you more stressed as it gets nearer or ends up that they won't be able to be there by then. Just think that you know they'll coming soon, and that's when you'll spend your Christmas with them. Once you are all together, the stress and hassle will all be gone!
