The more you show of your subjects, the harder it is to pose them naturally, so sometimes it's easier to sit them down. In the above photo, the couple are turned sideways, that's always a good start, the husband has his back to the tree with his legs apart and the wife is sitting between his legs.
I asked her not to sit down flat on her bum, but instead to roll onto her hip, that avoids her lower area 'squishing out' (that's a photography technical term!!). Also notice the way her arm is draped over her loving husband's knee, which shows the contact and relationship between them.
Use different angles
We see the world from our own viewpoint and height (obviously!!), so changing the camera angle or the camera position can have a dramatic effect because it's not how we usually see people and scenes. In this photo, taken outside in a park, I asked this pretty young lady to sit on a step, and I stood on one of the higher steps. I made sure I wasn't too close to her, as (apart from invading her personal space) getting in too close can create unwanted distortions.
I used a fairly wide aperture for this photo, around f2.8 to blur the background, and so kept the emphasis on her lovely eyes.
Try spreading out large groups
There's no law that says you have to put people in a line or in rows when posing large groups. Instead try positioning them separately into their respective smaller family groups with maybe some standing and some sitting. It looks better if they are not all doing the same thing or facing the same way, and gives more variety to the overall image.
Notice the way that some of them are leaning or resting against the pillars or steps, people tend to find that more relaxing than standing in an open area, and it tends to lead to a more natural looking pose.