Actually - you did a pretty good job. Your shots are sharp, well exposed, and the expressions we see here are all very good as well. All of those points are the base of a good portrait sitting. Now, when you continue, think unity of family. So hands and arms and heads all lead towards the center of the group, and keep spaces between family members to a minimum.
When you can tilt heads toward one another, do not cut off limbs, fingers, feet and always crop above a joint.
In the last shot for example, the daughter should be sitting on Mom's lap and the son real close to her with Dad (hands out of pocket,) shoulder touching Moms. Think of shapes the heads could make and set up those poses. "W" - "U" - "Circle".
But as portraits go I have seen MUCH worse. so keep plugging away. Get books on family portraiture, and study the actual positions of each member of the group.