You can simply create extra conditions which match the fields you require in the same function. For example, using your code above...
$(document).ready(function () {
$('#form').validate({
errorPlacement: function(error, element) {
//Custom position: first name
if (element.attr("name") == "first" ) {
$("#errNm1").text(error);
}
//Custom position: second name
else if (element.attr("name") == "second" ) {
$("#errNm2").text(error);
}
// Default position: if no match is met (other fields)
else {
error.append($('.errorTxt span'));
}
},
rules
});
Hope that helps!