four people walk down a sidewalk at night
People walk at night.
When the word people is being used, it generally means that it is more than one person. In this case the people are the ones walking at night!
exists e1 s1 x1 x2 x3.(at(e1,x3) & n_night(x3) & a_down(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_sidewalk(x2) & n_people(x1) & card_eq_4(x1))
exists e1 x1 x2.(at(e1,x2) & n_night(x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))