This is a default functionality that is available in our Magento 2 marketplace, for this admin must allow the Seller Manage Order as ‘Yes’.Now the seller can generate invoices for their ordered products, generate a tracking number and shipment for orders of their products.
Even the seller can notify the customers by sending them emails, cancel/refund the order and even print the order.
Refer to the below screenshot(the image is taken from Magneto2 marketplace), for mail notification template-
Please do contact us for any further queries or requirements. You can also check our Magento 2 Extensions for additional features.