Samuël de la Bella did not die in Seibersdorf in Poland. For Samuël to have died in Seibersdorf, he would have had to disembark the train when it stopped at Cosel. However, at 50 years-old, Samuël was on the age cut-off (which the SS arbitrarily set at 50 or 55, depending on the transport). Samuël stayed on the train with his wife and two children rather than disembarking at Cosel.
Samuël arrived at Auschwitz with his wife and two children, where he and his daughter Rachel passed selection.
Samuël appears in the Auschwitz Hospital Barrack book as prisoner 63507 and a date of death of 15 October 1942.
There is also an error with Rachel's date of death: she perished almost two weeks before her father, on 2 October 1942. Rachel had passed selection as well. The current date of death listed for her (13 Sep 1942) assumes that she was gassed upon arrival, however, she is in existing Auschwitz documentation, so we know that she perished as labor.
Lea and Joseph were gassed upon arrival on 13 Sep 1942.