.Events(e=>e.Edit("ganttEdit"))

<script>
    function ganttEdit(e){
       var tabstrip = 
       e.container.find(".k-gantt-edit-tabstrip").data().kendoTabStrip;
       tabstrip.bind("activate",function(args){
           if(args.item.textContent == "Other")
           {
              var otherForm = $(".k-gantt-form-other").data().kendoForm;
              var newOptions = otherForm.options;
              
              if(newOptions.items.length < 3)
              {
              newOptions.items.push({
                "field": "Role",
                "type": "string",
               "defaultValue": ""
               });

              otherForm.setOptions(newOptions);
              }
           }
       })
    }
</script>