Welcome to the Hive blockchain!
Witnesses are the people who run servers that keep the blockcain running. They're called "block producers" on some other blockchains, and without them, there is no blockchain.
Multi-accounting, or "account-farming" as we usually say here, is when an individual creates multiple fake-accounts to try to steal more from the Rewards Pool than is deserved. People who do that are too lazy to create good content as you have done here (BRAVO!), and try to steal rewards in other ways.
Be genuine & honest, keep producing good, original content, and you will have no problems on Hive.