Couple different ways you can go about it! 

If need be, you can be signed into multiple devices at once with your Square account. This would allow several people to have Readers and take payments at once; with all payments going to your account.

Alternatively, we offer Employee Management features that allow you to create employee logins and set various permissions for them. Read more about that in our Help Center. 

Hopefully that information is helpful! Lastly, if you do need additional Readers, shoot our Support team a message: https://squareup.com/help/us/en/contact