Creation Of Customer Groups in OpenCart Version 2.0

Hi, I have recently installed OpenCart 2.0 on my new onlinestore. I had asked the developer who did the installation to create a Special Customers Group that would be charged the wholesale price of $21.50 instead of the retail price of $28 once there are 12 items in the cart. He did not implement this properly. The mistake he has made is that he set it up in such a way that the Distributor must buy 12 packs each of ALL SKU's in order for the $21.50 to apply. A picture of his mistake is attached. I need someone to fix his mistake so that if they add a total of 12 packs of any or if they mix items as long as they ate buying upto 12 packs, the $21.50 will apply. So I need you to ( 1) check and ensure that this Special Customer Group was ever created in the first place, if it wasn't created at all, I need you to create it (2) I need you to check and ensure that all my distributors/wholesale customers have been added to this Special Group, if they haven't, I need you to add them. (3) I need you to implement this so that if they add only one item to cart or rather 11 items or less to cart, they are charged the retail price of $28 but it they add 12 or more items to cart, they are charged the wholesale price of $21.50 (4) I need you to teach me step by step how to add a new distributor to this SPECIAL CUSTOMER GROUP so that when I have a new distributor, I can easily add him or her to this Special Group by myself. (5). Lastly, I need you to work with our Fulfilment partner to ensure my OpenCart is hooked up with their ERP system so that once an order comes in, it is visible at their end and they can ship it. You will have to give them the info they require for this which you will obtain from my shopping cart or Cpanel such as the [login to view URL] files, XML Request Files, XML Response Files described in the PHP code etc. Let me know if you have any questions please. If you have never worked on OpenCart Version 2.0 or have never installed it, I kindly request that you please do not apply for this Project. Thank you.