We normally get an MSDN subscription. These licenses can be used for Dev, but
not production. You will need one license per virtual machine used by each
developer.

To set up developers environment, what licenses you need depends on if your
company is MS partner (Registered, Certified or Gold Certified) or end
customer.

If first, look at benefits, comes with partner program.

If not, you can buy MSDN licenses (FAQ about MSDN you can find at
msdn.microsoft.com/.../aa948864.aspx), which will be
enough for dev environment.

MSDN licenses are single user licenses, so every developer needs its own.
You may not use this software in production environment.