Here is how Waller, Flag, and Nighlock meet the recruits of Belle Reve and Dr. June Moone and Enchantress are introduced in Nighlock and the Suicide Squad.
[a plane lands]
(we see Waller, Rick Flag, and Nighlock walk into Bell Reve)
Nighlock: Dibs on meeting with Croc and Diablo.(seperates from them)
Rick Flag: I'll be waiting at the shooting range.(leaves)
Amanda Waller: Why leave me with the crazy one?
(she overlooks Harley)
Harley Quinn: Are you the devil?
Amanda Waller: I might as well be.
(we see Nighlock walk up to Croc's cell and knock on the bars with his bionic arm)
Killer Croc:(knocks and walks to him) Aren't you scared?
Nighlock: Me and my fellow mutants have been treated just as horribly as you are.
[we see Deadshot escorted to the shooting range]
Deadshot: So what is this? Cheerleading tryouts.
Nighlock: You could say that.(to Waller and Flag) I've got Diablo.(opens a portal to his cell and goes there)
[the government people turn to Deadshot]
Rick Flag: They say you never miss. Wanna test that?
Deadshot:(shoots the guns at the target)
(we then see Waller and some officials in a conference room, without Nighlock and Kelly)
[Enchantress demonstrates her powers and changes back into Dr. June Moone]