Please refer to https://skyvia.com/resources/docs/index.html?account_users.htm ("Inviting and Deleting Users from Account" section).
The invitation emails are not sent in this case. When the invited user logs in to his Skyvia account (or signs up, if the users is not yet registered), he can choose whether to use his default account or the account of the user that invited him.
Please note, a user cannot have access to packages, connections, and stored queries of other users, sharing the same account. This allows limiting access of different users to the company data.