what happens during the selection process held on the third day of the prisoners' journey from Buna ?

At dawn on the third day, Elie rushes to bring his father from an SS selection. THere is chaos at the selection site. Survivors and victims blend together. The guards are entertained by Jews eating snow from each other's backs. The guards watch them scrambling for crumbs and eating snow late into the evening.

how Elie's Family were separated?