I pretty much just use the "Interact with target button"". You can iether use 2 buttons or a round robin for the assist then the button. I then drive with my main character and just use the button to get the slaves to loot. It is totally random but as one slave completes the quest then you just continue to fill up the other slaves. Just watch your quest tracker to see whenn all the slaves have completed the quests then complete with the driver. I leave the driver for last so he can easily see if there is still anything on the corpse as indicated by the glitter effect. If so just hit button again and the one of the other slaves will loot the item.

Has made the collection quests alot more doable for me but still a pain most of the time.