How do I make a javascript call based on the value of two textboxes?

Let do it together:
1. in the form tag, modify the onsubmit event, when the return is false, the submit will be cancelled

<form method="post" action="" onsubmit="return check()">

2. add ids to the input texts for myparents and yourparents, so that we can access them in javascript function later on:

<input type="text" id="myparents" class="validate[required]" />

<input type="text" id="yourparents" class="validate[required]" />

3. Now, write the check() function:

<script type="text/javascript">
function check()
{
   var myparents = document.getElementById("myparents").value;
   var yourparents = document.getElementById("yourparents").value;

   var status = true;
   if (!myparents.trim()) {
      alert("My parents cannot be blank!");
      status = false;
   }
   if (!yourparents.trim()) {
      alert("Your parents cannot be blank!");
      status = false;
   }
   return status;
}
</script>

The End.