These three Thugs are only encountered during a so-called Random Encounter during the Baldur's Gate II: Shadows of Amn campaign. It occurs sometime after encountering the bounty hunter Suna Seni and her group of Slavers.
While transitioning between Athkatla's Districts, the party will inevitably encounter this group of Thugs, which includes a Fighter (ReThug01.cre), Cleric (ReThug03.cre), and a Thief (ReThug04.cre). An unnamed Mage (ReThug02.cre) rounds out the group.