How customers can create sub accounts in Magento 2 mobile app?

You can use Magento 2 Customer Sub Account module to get the feature in Magento 2. The module allows the customer to create multiple sub-account users and gives different permissions and accesses to manage and view information of the main customer account.

Once you have the feature on Magento it can be integrated into Magento 2 Mobile app through customization. For this, you can contact us by creating a ticket.