I am helping a friend to research her family and this is my first adventure in Eastern European genealogy so I'm looking for a bit of help.

Katerina Shytosh (spelling could be incorrect, I was told the name is Hungarian) was born about 1913. Her family was from Pančevo, South Banat, Vojvodina, (Ukraine/Yugoslavia). She married a man named Theodore Gretschiskin / Greychiskin / Grechkan who was born in Russia and was a member of the Russian Army. This was sometime just before or during WWII. Katerina's father was a Ship Captain and he and his wife and 12 children (6 boys and 6 girls).

Theodore wanted to join the Russian Army at age 16 but was told he had to get married. He married an older Russian girl (name currently not known) and joined the army. He was searching for his father, who was also in thye army. Other soldiers told Theodore that his wife had been unfaithful, so he met Katerina Shytosh and married her.

Theodore had at least 3 children but I'm not sure if they are bilogical children of his first wife or of Katerina. The children are: Helena, Maria and George. Helena was born sometime around 1935-1940 and married Miroslav "Mike" Stefanov who was likely from Russia. They emigrated to Brazil at some point and then to Canada. Maria and George were living in Sao Paulo, Brazil after leaving Europe.

Any help or hints would be very welcomed.

Thanks!