Professional photographers must have a lot of patience. When the twins were nine months old, I took them to a professional photographer and had portraits done. The pictures were decent. No crying. No temper tantrums. And the kids look pleasant even if they aren't giving their best smiles.
Since then I haven't been brave enough to try a professional sitting. Especially given the chaos that ensues when my husband pulls out his camera. We still get good shots of the little one as she can't move yet. (Well, that was yesterday. She has now found warp-speed for crawling.) When the twins see the camera, they want to see themselves on the display screen. But they can't see the screen and be on it at the same time.
The other problem is that they want to take pictures themselves. They search for their cameras which means they are not available for our photos. They eventually find their digital camera - a Matchbox size camera I found at Walmart for $15. My son likes to put it in his pocket, and needless to say, I have washed it too many times for it to ever take pictures again. They also pull out their phones and take pictures with those. So we get a lot of pictures of their phones or their camera in front of their faces. Not quite the image I want to frame.
A recent attempt at getting a picture of all three children resulted in ninety pictures with one child in them and a portion of the other two. Or one child looking at me and two looking at someone else. We were outside, so I had the little one on a blanket and the twins on their lawn chairs. I positioned them on one corner of the blanket and went to the opposite to take pictures. The twins followed dragging their chairs. I'd get the twins back in position and the little one would turn around to look at them. I either got a decent - and by decent I mean I could see their faces, not that they were smiling - pictures of the twins and the back of the little one's head or the little one alone with a concerned expression on her face.
On the positive side, I was using a digital camera, so no film to develop and I wasn't paying a sitting fee. Thank goodness for Photoshop.