An LSP.expert team can have as many members as you wish.
To add a new user, simply click on 'Add a user' under Settings > Users, roles and permissions.
In the popup that opens, you will have to enter the name and the email address of the new user + the role you would like to give them in LSP.expert.
Once you added the user, they will receive an email asking them to join the team.
To manage your roles in LSP.expert, see this article: https://help.lsp.expert/en/articles/2558507-can-i-manage-the-permissions-of-the-users-in-my-team