The problem is that you're having multiple identical IDs - use class instead and change ID based on row number or some other criteria so that each row has unique calendarID. You can do this server side in OnDataBound event.
Add the class .datepicker-repeater to item template.
e(document).ready(function () {
e(".datepicker-repeater").datepicker({
changeMonth: true,
changeYear: true
});
If this helps please take time to accept the solution. Thank you.