Several small children are playing basketball.
Siblings are playing.
You can not infer they are siblings.
exists e1 s1 s2 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_basketball(x2) & n_child(x1) & a_small(s2) & Theme(s2,x1) & a_several(s1) & Theme(s1,x1))
exists e1 x1.(Actor(e1,x1) & v_play(e1) & n_sibling(x1))