Euribor is not a rate that central bank lends to other banks, it is a rate commercial banks lend between themselves.

ECB has its own rates (e.g. deposit facility, marginal lending facility for overnight deposits and loans).

As I mentioned somewhere else, these loans, are based 100% on bonds, sold on the open market, so the issuer is not loosing money. The issuer “realkredit selskab” just gets a fee.

Who buys the bonds, could be anyone.. banks, pensionfunds, people who need to store money, in an “insured” way.