display two related product module in each product page

Hi,

There is no easy way to do that.
It would require developping a custom plugin to add such extra option to the product edition interface using the onHikashopBeforeDisplayView trigger, then add an extra option to the module edition interface using the same onHikashopBeforeDisplayView trigger, then handling the saving of the first option in the onBeforeProductCreate and onBeforeProductUpdate triggers, and finally, add the filter on the product loading query for the modules with the option activated using the onBeforeProductListingLoad trigger.