Just as you do not want the exposure to change from frame to frame, neither do you want the focus to be adjusted. Assuming you’ve taken #1 to heart and are using a tripod, you will not be moving. Likely if you’ve posed your group in a relatively static position, they will not be moving. Not much anyway. We are only concerned with moving closer to, or further away from the camera. So . . .
In real estate it’s location, location, location. In photography it’s quality, quality, quality. When you are looking for a photographer, you want to look at their exposure, white balance, and focus. Is it all correct and consistent? Before you inquire with a photographer on pricing information, you want to make sure that you will receive quality images. Some families get photos done yearly. Some only get them done every few years, or just once when their kids are little. No matter how often you get photos done, these images will be hanging on your walls, in frames at your office, and in albums that many generations will get to enjoy. Making sure you have a photographer that can deliver you images with correct exposure, white balance, and focus should be top priority.
There are a few bonuses to using accessories well (as well as layers). One is that changing them up a bit throughout the session can give you multiple looks without having to do many wardrobe changes. They can also be something that the subjects can interact with. A sassy little tip of the hat, holding the ends of a scarf while running and letting it billow behind you, grabbing the lapels of a husbands jacket while pulling him close for a kiss – all these little gestures and ways to interact (and become more comfortable in front of the camera) can be made possible with styling choices. Many of my sessions will feature items used outside their intended use or subject. My girls are often seen in mommy’s hats or scarves (scarves can be used in different ways like wrapped around their shoulders, as a hair piece, etc) and they love to wear my costume jewelry.