when working with a multiple checkbox, the selected items are added to an array.
you need to use the implode(); function to convert the array to a comma separated list.
in the code to display the checkbox values, you have:
$MailBody = $MailBody . ((isset($_POST["Other_services_group_Enquire_about_our_other_Chandelier_Group_services_tick_box_to_select[]"]))?$_POST["Other_services_group_Enquire_about_our_other_Chandelier_Group_services_tick_box_to_select[]"]:"");
this needs to be changed to:
$MailBody = $MailBody . ((isset($_POST["Other_services_group_Enquire_about_our_other_Chandelier_Group_services_tick_box_to_select"]))?implode(", ",$_POST["Other_services_group_Enquire_about_our_other_Chandelier_Group_services_tick_box_to_select"]):"");