This doesn’t entirely answer your question but I visited the cemetery at Diemen, a suburb to the east of Amsterdam, last year. Very easy to find and walk around. There were just a few graves from the 1940s and I possibly would have seen your relative’s.
You could phone them up to ask your questions. They should have records of who ordered/paid for the funeral.
My relative, whose grave I was seeking, died in 1938 and was taken from the Metaarhuis which was at the rear of the Jewish hospital near the centre of town. It was from there that Jewish dead bodies were transported. I have some pictures of this place, now just houses, which sport some plaques, and also of the cemetery. I would happily forward them to you.
Carole Shaw, London UK
WOLFSBERGEN, BOSMAN: Holland
ZANDGRUNDT (plus variations), SANDGROUND: Warsaw, London and beyond
JACOBOVITCH/JACKSON: Staszow, Poland & London
KOSKOVITCH/KENTON: Staszow, Poland & London