Currently, Magical Make an Offer only sends offer notifications to the main store email address. There isn’t a built-in way to send notifications to individual sellers or to limit access just to the products they manage.
If you want your sellers to manage offer requests, you could give them Staff access in Shopify. However, keep in mind that staff will be able to see all offer requests, not just those for their own products. There is no way to restrict this further within the app at this time.