In view of Klein's intense closeness to his family, the first few months in Terezín without his mother and sister must often have been distressing. Pre-printed postcards did occasionally reach Prague from Terezín, and Czech gendarmes could be bribed to deliver messages back and forth, though these channels carried huge risks. In short, whether he was able to keep in touch with his family is unknown. But on 20 July 1942 Ilona and Lisa arrived in the camp on Transport AAS from Prague. The period leading up to their departure was tense. ‘In that time, I was desperately looking for a lawyer for my brother-in-law who was sentenced to death’, Lisa recalled. In fact, for a short while before his execution in Munich in August 1943, Jaroslav Dolak was imprisoned at Terezín, in the Gestapo prison, known as the Mala Pevnost (‘Small Fortress’), across the river from the main ghetto. Lisa explained that she and Ilona prepared to leave their home:

Klein's aunt Reginka arrived a few days after Ilona and Lisa. Other members of the family were in Terezín, too, if only briefly, en route to their deaths. The Kulkas from České Budějovice arrived for a few days in April 1942, before being deported to the Izbica ghetto. Aunt Eliška, uncle Vítězslav and their daughters Hanna and Zuzana died in Izbica, and Hary and Arnost were murdered in Majdanek later that year. Additional relatives made brief appearances. Klein's aunt and uncle, Julius and Anna Marmorstein, along with their children Karel and Milan, arrived in Terezín towards the end of June 1942, but by the middle of July had been murdered in the Maly Trostenets extermination camp, south-west of Minsk. Aunt Isabela, whom Lisa remembered with such fondness from the Přerov days, was also in the ghetto. Isabela's sister, Paula Schenk, and her husband, Jindřich, arrived on the same transport as Julius and Anna, but were then transported to their deaths in Treblinka in October.