Complex sentence: Gavrilo Martsenkovich known as "Gavrilushka" was Russian an opera actor and singer in 18th century from the group named "pevchie" (the singers) of Count Razumovsky.
Split into simpler sentences: Gavrilo Martsenkovich known as "Gavrilushka" was Russian an opera actor and singer in 18th century. He was a member of the group named "pevchie" (the singers) of Count Razumovsky.