COOPMAN Spelling may have been Koopman

John Coopman of Buffalo New york in 1865 may have spelled his surname with a K(Koopman). Father was Cornelius Koopman. Mother was Mary. Sister was Mary who married a Vanderhoff. Vanderhoff's daghter married a vanderwerf. Mary Koopman may have been born in Bolsward. Her birth year was 1868. I need help looking for roots. Thank you.