Hi,
you can't give all three buttons the same instance name, 'cause then Flash will only target one of them, which in this case is the first button! Give the other two a unique instance name, like click_item_btn2 and click_item_btn3, this is essential!
and then simply copy and paste your first button's actionscript to the other two buttons, like this:
Actionscript Code:
create_item_btn2.onRelease = function()
{
createInventoryItem();
}
create_item_btn3.onRelease = function()
{
createInventoryItem();
}