Two women are singing on a stage while a man in red plays the guitar.
Two sisters sing while their brother plays guitar.
Two women does not necessarily mean sisters.  A man does not imply being a brother.
exists e1 s1 x1 x2 x3 x4 x5.(while(e1,x3) & n_guitar(x5) & (x3 = x5) & in(x3,x4) & n_play(x4) & a_red(s1) & Theme(s1,x4) & n_man(x3) & on(e1,x2) & n_stage(x2) & Actor(e1,x1) & v_sing(e1) & n_woman(x1) & card_eq_2(x1))
exists e1 p1 x1 x2.(exists e2 x3.(Theme(e2,x3) & Actor(e2,x2) & v_play(e2) & n_guitar(x3)) & n_brother(x2) & of(x2,x1) & n_thing(x1) & while(e1,p1) & Actor(e1,x1) & v_sing(e1) & n_sister(x1) & card_eq_2(x1))