Perhaps I am not understanding this scenario as you intended, but it does not sound like you would need to use the "kit" option in our Inventory system in order to do what you described here.
If you are posting several of the same product in the same listing and you want to use our Inventory system to keep track of the quantity you have left, you should just need to create one inventory item for the item and post the listing with the quantity that you would like to offer for sale.
When you post the item to eBay, the quantity left in inventory will be initially reduced by the number of the item available for purchase in the listing. Then, when the listing comes to a close, the quantity available in the inventory item will be replenished by the number that went unsold so it shouldn’t matter if some buyers purchased two of the items and other purchased one.
If you have any other questions about this, or anything else related to your account, I recommend contacting our customer support team using the form on the following page of our site: http://www.auctiva.com/help/requesthelp.aspx#