The early flight testing should have had happened at Rechlin and Peenemünde (Luftwaffe airfield) but there might be many facilities and separated sites to build parts elsewhere. Did your father have some very unusual qualification that made him especially valuable for aircraft equipping?
It was truly shameful how people were treated in some if not most german arms factories back then. Conscripts were sort of only slightly better off but they even forced concentration camp prisoners to slave labor like for V-2 production at Mittelwerke and Peenemünde. People got hanged or shot for nothing and SS who administered this received the slave labor payments.