Hi,
For the addition of the "sold by vendor" in the email ; I implemented the feature for HikaShop 2.3.5 + HikaMarket 1.5.1 (the next versions).
It requires some modifications in the HikaShop emails but I made something generic that other plugins could use to display some extra data in the HikaShop notification emails.
(I will see with Nicolas in order to validate my proposal).
About the invoices, I will require more details about which invoice (user front-end ? backend ? vendor front-end ?)
It might be necessary to create a view override in HikaShop in order to display the vendors ; I'm not sure I will be able to use a trigger but depending your requirement.. Maybe.
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.