Messrs Onwumere and Anagor will be on supervised release for five years and will repay the victims.
Mr Ogbata, scheduled to be sentenced on April 14, faces a maximum penalty of 20 years in prison.
Amos Prince Okey Ezemma, 50, was a member of a group of fraudsters that sent personalised letters to elderly victims in the United States.
Kofi Sarfo is a medical doctor and a Las Vegas hospital owner. His wife, Rose Sarfo, is the office manager and treasurer.
Jerry Chucks Ozor, 43, and Iheanyichukwu Jonathan Abraham, 44, were part of a group of fraudsters that sent personalised letters to elderly victims in the U.S.
