In order to get all of your colleagues (developers, product managers, legal, etc.) access to the correct Site, you'll need to invite them to join by their email address. Note: Your email address can work across many accounts and Sites! All Sites and Accounts you have access to will appear in the dropdown in the upper right hand corner of the screen: 

Inviting a Member to your Site

To get a new member setup on your Site, go to your Site Settings and you'll be able to invite users from the Members tile:

Then enter the email address of the Member you'd like to invite and they'll receive an email. Note: existing users will see the Site added to their Site dropdown the next time they login so they don't need to do anything at all!