We sync the images from Shopify, these can be changed within Shopify Admin but not in the app. There is a request to allow the seller to 'choose' which images are sent to the app but this is not yet developed.
Only one image is shown for my VC (variation child) product
Shopify flow of VC images works differently to Target. Target have multiple VC images and one VAP image, whilst Shopify add multiple VAP images but only one VC.
For further assistance, please reach out to marketplace-connect@shopify.com