Perhaps, but in my mind I am seeing a balanced shot... guy on one side, girl on the other, boy in middle; and I am thinking parents and kid. Just my opinion.
Maybe..... young man on one side, leaning with shoulder into tree, arms folded, foot crossed (hard to describe that, but I am sure you know what I mean), with the girl on the other side, back
slightly to tree, and hand on son's shoulder?
the boy close to mother, and then maybe on opposite side of his mother. He will still be in contact with her with a slight space between brother and sister.
Not a lot of space between the brother and sister... don't wanna make it appear they dislike each other.
Yep.. a tough assignment , but take your time, and you will do fine.