PHP expects t1, t2, t3

$firstname = $_POST['t1'];
$middlename = $_POST['t2'];
$lastname = $_POST['t3'];

you are trying to send variable name 3 times

sendData_lv.name = t1.text;
sendData_lv.name = t2.text;
sendData_lv.name = t3.text;

you need to change this to -

sendData_lv.t1 = t1.text;
sendData_lv.t2 = t2.text;
sendData_lv.t3 = t3.text;