It was quite gruesome to figure out, one feels like some sort of a bookkeeper when describing the events. The biggest part (about 40 ppl) of my family was arrested during one single razzia on the 18th of April 1943. They were betrayed by their neighbour. After torture the sites where the rest of the family in Rotterdam was hiding were revealed and consequently raided on the 22nd, 25th of April and the 2nd of May, all in 1943.
After a short stay in the "Hollandse Schouwburg" (Dutch Theatre - collection site of Amsterdam Jews and Jews from other parts of Western NL), they were herded to the Amsterdam Muiderpoort trainstation on the 10th of May 1943 and packed in the trainwagons we all know. The train went first to Bergen Belsen, where they presumably arrived on the 12th of May.
There half of the wagons were cut loose from the train and the ppl in there were herded into the Bergen Belsen camp, among which app. 40 family members. These were to stay for a few months in Bergen Belsen, before being shipped to Auschwitz, where they arrived on the 12th of September 1943.
It seems they weren't killed immediately, but for certain not long after arrival as records indicate that two weeks later new shipments from France and elsewhere arrived and there was ample space to hold them - the numbers of inmates two weeks earlier imply that nearly all of the barracks must've been full to the limit. It's therefore safe to assume that they were killed somewhere between the 12th and the 27th of September of 1943. The Nazis didn't keep names and numbers of the loads that went into the gaschamber, so it's hard to determine on which day exactly they were gassed.
The remainder of the train with app. 35 family members in it went from Bergen Belsen on to Treblinka, where they arrived around the 25th of May 1943. Everybody on that train went straight from the train into the gaschamber. Yet it's impssble to name exact dates of which one was gassed on which day as, like I said, the Nazis didn't keep books on that particular part - at least, I didn't find them.
Edit: have to add that my private research was only pssble with the friendly co-operation of German, Polish and Dutch authorities in the field.
M-G (like I said, I felt a bit like a bookkeeper checking on his books)