$('.check-opt').change(function () {
  if ($('input[name="step_2"],[name="step_4"]:checked').val() == "yes") {
    $('#order_btn_id').removeClass('disabled');
  } else {
    $('#order_btn_id').addClass('disabled');
  }
});

var disabled = $('.check-opt:checked').length == 0;

var a = $('input[name="step_2"]:checked').val() == "yes";
var b = $('[name="step_4"]:checked').val() == "yes";

$('#order_btn_id').toggleClass('disabled', a || b)