Here is what I found on Russian site:
"Engel Yakov Ivanovich, of German nationality, born 1920, in village Grafskoye, Fedorovskiy District, Rostov Oblast. He was arrested by military on 04-22-1943 under Rusian law. He got 6 years of jail and also got the loss of his rights for 5 years".
That would meen that his father's name was Ivan.
Could he be those siblings child?