Complex sentence: There were ten staff members, each with a specialty (finance, agriculture, etc.), and the area itself was divided into the Courland District, the Lithuania District and the Bialystok-Grodno District, each overseen by a district commander.
Split into simpler sentences: There were ten staff members, each with a speciality (finance, agriculture, etc.). The area was divided into the Courland District, the Lithuania District and the Bialystok-Grodno District, each overseen by a district commander.