<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<div class=test>
<input id='inTest' name='val[]'>
<input id='inTest' name='val[]'>
<button type='button' id='add'>Отправить</button>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script>
$('#add').on('click', function(){
$(this).siblings('input').each(function(){
alert(this.value);
});
});
</script>
</body>
</html>