For your first dropdown
<a class="btn btn-navbar" data-toggle="collapse" data-target="#first">For your second dropdown:
<a class="btn btn-navbar" data-toggle="collapse" data-target="#second">Then you can add that unique id to your nav collapse container:
First
<div id="first" class="nav-collapse"> ... </div>Second
<div id="second" class="nav-collapse"> ... </div>