Library Expansion Options Licenses

Hi,

i read the Licensing Guide, but now it is not clear for me how many licenses i will need:

Configuration:
2 Media Servers and 2 Tape Libraries with 1 Drive
Each Media Server can use both Tape Libraries

Do i need 2 Server Licenses + 2 Library Expansion Options or is every Library licensed by the Server License?

When I add 1 Drive to 1 Library in this configuration, do i need 2 Library Expansion Options, 1 for each Server?

Thank You!