
Not a breeder, but this is what the breeder did when I got my latest dog two years ago.
My pup was from a litter of ten. They kept three of the puppies (had only wanted one, but there you go

) and each of the seven remaining pups were allocated a day to leave and in the morning so that they would have time to settle in the new home.
The previous day, the pup that was going to leave would be brought back into the house to get used to being indoors again. They had spent the last two weeks in an outdoor run because it was so warm even at night - they are a large Gundog breed. The night indoors gave them the oppourtunity of living with the older dogs including mum and being taught a few lessons in acceptable behaviour.
When we arrived to pick her up, she was very relaxed. The older dogs were gradually taken from the room, including mum and we had the final handover etc. When we actually left, it was only the humans that came out for final cuddles, photos and a few tears.