How to have at least two datepickers of ui-bootstrap on a single page?

Rather than using a different function you can use a different is-open attribute and then pass the attribute in through the ng-click function. You still need different models:

<div>
        <div class="form-horizontal pull-left">
            <input type="text" datepicker-popup="dd-MMMM-yyyy" ng-model="dt1" is-open="opened1" min="minDate" max="'2015-06-22'" datepicker-options="dateOptions" date-disabled="disabled(date, mode)" ng-required="true"/>
            <button class="btn" ng-click="open($event,'opened1')"><span class="glyphicon glyphicon-calendar"></span></button>
        </div>
        <div class="form-horizontal pull-left">
            <input type="text" datepicker-popup="dd-MMMM-yyyy" ng-model="dt2" is-open="opened2" min="minDate" max="'2015-06-22'" datepicker-options="dateOptions" date-disabled="disabled(date, mode)" ng-required="true" />
            <button class="btn" ng-click="open($event,'opened2')"><span class="glyphicon glyphicon-calendar"></span></button>
        </div>
        <button type="submit" class="btn btn-default">Submit</button>
    </div>

And inside controller:

   $scope.open = function($event,opened) {
    $event.preventDefault();
    $event.stopPropagation();

    $scope[opened] = true;
  };