I am sorry but to keep our sales fair we have restricted each customer to a maximum of 2 copies of any product. These must be placed as 2 separate orders.
Additionally, some products are locked down even further to just one copy per person. This is to enable our limited stock to reach as many different users as possible.
I have multiple family members though!
If you have family members sharing a computer you might benefit from using Steam Family Sharing, a free facility to use one key for multiple family members. Click here for more information.