I think going straight for the piscean is a good idea.
Other than that, my recommendation would honestly be to get one of all the options we've got. So a hand flamer for Whisper the juve (I see you already have a web pistol, that's good).
You should definitely get a nacht-ghul with Serpent's Fangs. Instead of or in addition to your existing nacht-ghul is up to you, I don't think having 2 with different weapons is overkill at all. Speaking of nacht-ghuls, getting armoured undersuits for it/them is big value, people will often try to murder them, and they're pretty fragile for a melee dude.
If you can find the credits, a champion with a smoke grenade launcher is big value.
Since you are using a flechette pistol on your leader, you should definitely get a chem-synth for your leader. It adds +1 to your toxin roll, which is great for obvious reasons.
If the gangers can use trading post ammo(I'm unsure), you should get a shotgun from the house list and buy executioner from the trading post for it.
Personally I really like a psy-gheist with Unrememberable Utterance on it.
Should probably add a ghost with a lasgun, they're great.