People gather together in an art gallery.
people are at their relative's exihibition
People can be at an art gallery who have no connection to the artist, and there is no reason to infer that this is their relative's, or that there is even an exhibition going on.
exists e1 p1 x1 x2 x3.(in(e1,x2) & n_gallery(x2) & of(x2,x3) & n_art(x3) & exists s1.(Theme(s1,x1) & a_together(s1)) & Topic(e1,p1) & Actor(e1,x1) & v_gather(e1) & n_people(x1))
exists p1 x1 x2 x3.(at(x1,x3) & n_exihibition(x3) & of(x3,x2) & n_relative(x2) & of(x2,x1) & n_thing(x1) & n_people(x1))