Harry,
Study and pray because when the time comes and the family is standing there you'll forget everything you were supposed to do
I usually start with one person, the tallest (normally Dad) and pose him at a 45 degree angle to the camera. Then I add Mom close to him (they are after all in love) again at a 45 degree angle then the next tallest child (at 45 degrees) then the next etc. Make sure no two heads that are side by side are the same height and make sure no two heads are directly above/below another (stacking.) Don't crop at the joints. Don't stand Dad then seat everyone else on the floor as his head will be five feet above everyone elses and look really strange. All the heads should be within a reasonable distance from one another.
Benji