many people from eastern european countries did indeed join various divisions of German army or more likely SS; divisions from partner countries (ie rumania) did also fight alongside German units, HOWEVER, Stalingrad was encircled due to russian counterattacks on the flanks which broke through mainly rumanian held areas (because these areas were known to be significantly weaker) and thus led to the well-known military disaster from the German point of view.
I´d also question the idea of "brethren", what do you mean by this?