IS-LM , Eurozone and Interest Rate Parity
It’s the same currency and interest rate structure for all countries. The only difference is that there is a default premium for some countries. You see the exact same thing in Canada, with the Canadian provinces trading at different yields.
The ECB is literally the union of all the national central banks. When the ECB makes a decision, it is implemented at the national central bank level.


The IS/LM model has severe limitations. The ECB sets interest rates; it’s ability to control “the money supply” (which aggregate?) is debatable. (It can increase the size of the monetary base, but that does not imply that bank deposits etc. will grow.)