Well, the problem is how you are selecting them in jQuery and how you have\ named them in HTML.
You should not use the same ID several times, use classes instead. When you use same ID for multiple instances, then HTML DOM model only accepts the top most element, or the first element.
so change:
<form id="addItem" action="addBasket.php" method="post">
To
<form class="addItem" action="addBasket.php" method="post">
and in jQuery do:
$(".additem")
It will work.