A group watching two men in white shirts perform.
There is a group watching two women in black shirts perform.
Unless these are two different groups, or the men and women are performing together, both men and women cannot be watched together. Also, sentence 1 is grammatically incorrect: A group IS watching two men in white shirts perform.
exists e1 e2 s1 x1 x2 x3 x4.(Actor(e2,x1) & v_perform(e2) & Theme(e1,x3) & Actor(e1,x2) & v_watch(e1) & in(x3,x4) & n_shirt(x4) & a_white(s1) & Theme(s1,x4) & n_man(x3) & card_eq_2(x3) & (x1 = x2) & n_group(x1))
exists e1 e2 p1 s1 x1 x2 x3.(exists p2 x4 x5.((x4 = x5) & n_group(x5)) & Topic(e2,p1) & Actor(e2,e1) & v_perform(e2) & Theme(e1,x2) & Actor(e1,x1) & v_watch(e1) & in(x2,x3) & n_shirt(x3) & a_black(s1) & Theme(s1,x3) & n_woman(x2) & card_eq_2(x2) & n_thing(x1))