Hi,
Multi Variant Custom Fields work based on Child-Products <-> Parent Product correlation (thus AJAX Loading is triggered when a selection is made). You can't load these custom fields on category page. Everything will be messed. Shoppers won't select the variant on category page properly, you will get loads of wrong orders -- it is much safer to not show them at all on category page to avoid confusion -- it is actually how our templates are developed. There is a note says on the add to cart button that says: "Select a Variant" and once the add to cart button is clicked; shoppers are redirected to product details page to make their selections
Regards