Three construction workers digging a hole.
They are digging.
Three construction workers are multiple people. You can refer to multiple people as "they."
exists e1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_dig(e1) & n_hole(x3) & n_worker(x1) & of(x1,x2) & n_construction(x2) & card_eq_3(x1))
exists e1 x1.(n_thing(x1) & Actor(e1,x1) & v_dig(e1))