shopify creating new skus when grouping product variants

[craftywool]

We are using EposNow to manage our products and stock control. It created the SKUs and barcodes for each of our products and we've successfully imported them into Shopify.

Our problem is that, for example, Product A comes 4 different colours (each colour has its own SKU and barcode generated by EposNow and is imported into shopify), the only we we can see to group these together is to select one and add the other 3 as variants, but Shopify treats these variants as new products and creates new SKUs for each which do not match our epos system for stock control etc.

We want Product A to be the main item when searching on the site but for it to show the other 3 variants at the same time but with the EposNow details.

How do we group these together without the new SKUs being generated?