Family photos are a little bit of chaos. And that's how they should be.
When I first started taking family photos many, many moons ago, I had no idea how to control the chaos that is taking children's photographs. The more young children you add to a photo, the more the chaos will multiply. The baby won't nap the day of family photos. You won't be able to explain how she knows, but she knows. One of the kiddos will run into a wall and bruise their forehead, or fall off their bike and scrape a knee the night before. Two of them will decide that today--just today, not any other day--they don't want their picture taken, or they only want it taken if they can choose where they stand, and how they pose.
As the parents, we stress over the outfits. The hair. Will it be too hot or too cold out? Are the flowers still in bloom? Will it be muddy? Will my kids behave for one hour. Just one hour, please. Kiddos feel that stress in a different way. They feel put on the spot, all eyes on them, mom and dad worried about their behavior, telling them to smile. "No, not that smile. Your normal smile. Why are you sticking your bottom teeth out?" Sigh. It's a lot for everyone.
But it really doesn't have to be. I try to tell every family who apologizes in advance for how chaotic they feel that it won't look that way. There will be three kids running around behind me while I take individual portraits, but you won't know it when you hang the pictures on the wall. You will see the gap in your child's smile when they lost their first tooth, the way their one ear sticks out a little like your Grandpa Bob's, that cowlick that won't stay tamed no matter how hard you try (but somehow in pictures it looks like it was always supposed to be that way).
So lean into the chaos for one hour. I promise I'm not stressing about it and neither should you.