Hi you need to be rather more specific, what you appear to be asking is how you put two Auctiva scrolling galleries (which bear in mind would contain the same images) at the top of your eBay shop and not the Auctiva store front.
There would not be enough horizontal space in a listing let alone anywhere else to support two SG side by side anyway.
Cannot see that what you are asking is remotely possible as the ebay store is totally seperate to the Auctiva storefront.