Hi,
I am sorry but the current version of plugin "attach serial" can't display two serials in one single image.
The plugin has been made to create one image per targeted HikaSerial pack so when the plugin is called only one serial is accessible ; and like that, I really don't see how we can modify the plugin to manage several serials in a single image.
It will require a re-development of the plugin.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.