Auto download orders from Ebay, Amazon and own website and synchronise all selling channels

Hi We have a Excel based Inventory control where each item has an SKU with INVENTORY IN and INVENTORY OUT and a column for Balance of stock. Orders are downloaded on .csv files daily and the Physical stock is adjusted for Pending Orders and updated manually to Ebay, Amazon and own website. We now want to automate the process so that a Worksheet on our existing workbook is updated with auto download of orders at periodic intervals and updated stock is uploaded on the respective websites automatically. The process has to happen every time a order is received on any Channel so that the stocks on all the selling channels are always syncronised.