You can code like two input box inside one div
<div class="input-group">
<span class="input-group-addon"><i class="glyphicon glyphicon-user"></i></span>
<input style="width:50% " class="form-control " placeholder="first name" name="firstname" type="text" />
<input style="width:50% " class="form-control " placeholder="lastname" name="lastname" type="text" />
</div>