My style for capturing extended families is a lot like that of my regular family sessions. We do lots of natural posing and breakdowns for each smaller grouping, cousins, grandparents, siblings, the whole bit.
We also have fun. Keep it natural. Incorporate some fun activities like preparing a meal or opening presents or playing a game. After all, some of the best photos we cherish of our families are those that capture their spirit through the way we connect with them.
That means, yes, grandpa can hold his martini and yes, dogs are family, too.