Hi,
I'm asking you since (almost) the beginning of that thread more details about your configuration.
But if you don't want to share it I don't know how I can help you.
The notification email to the customer should be automatic when a vendor change the order status and the main order is also changing.
If there are several vendors (several subsale) and the main order status does not change ; the mail won't be sent.
There is no magic in HikaMarket just logic !
It's not because one single vendor say that his order is shipped that the all content of the order is shipped.
Because the vendor might not have the all content of the order in is sub order.
Do you get the point ?