Not what I'd hoped to be doing, but study notes don't write themselves. (Dammit, school, don't you know I have more important things to be doing?)
Weiss
Abilities: Energy blast, shockwave, invulnerability, superspeed (may have been enhanced by Omega), cloning, SND
Notes: I still hold to the belief that Weiss has some undisclosed ability that sets him apart from the other Tsviets, though I have no idea what this might be. Weiss's advantage over the other Tsviets is that he seems to possess all of the 'general' abilities, and then a fair amount of sheer power on the side. Based on the Restrictor's comment about Shelke being the only one capable of 'this impressive ability' (SND, from context, though Shelke isn't wearing a helmet at the time... So I guess it's a possibility that he was talking about Shelke's hacking skills or something), I'm tentatively of the opinion that there's something about Weiss's SND skill that's different from Shelke's. Weiss's claim to superspeed is also up for debate, as he was Omega-enhanced at the time and Vincent was pulling similar stunts.
Nero
Abilities: Energy blast, cloning, invulnerability (temporary), Oblivion
Notes: I wonder whether there are some experiments that just don't 'take' with Nero, for some reason. It seems odd that he's the only one of the hard-hitting Tsviets without some kind of shockwave ability. The nature of his invulnerability also sees me groping for some explanation. I'm not sure whether to pass it off as a similar thing to Weiss and Azul, or whether this is yet another effect of Oblivion. I'm leaning towards the first, only because there's got to be a limit to what Oblivion can actually do.
Rosso
Abilities: Energy blast, shockwave, cloning, superspeed (debatable; see her meeting with the WRO soldiers in Edge), insanity
Notes: OK, so 'insanity' probably isn't the best word to use, but I do think that whatever experiment was conducted on her is the reason she's a coloured Tsviet. Deepground probably wouldn't care if the subject was unstable as long as it made them into a killing machine. I believe there was a similar sort of thing in one of the Halo books, interference with the ordinary chemical balance in the brain in order to boost adrenalin levels or some such. As I recall, this boost increased the soldiers' speed and strength and helped block pain, but also led to emotional instability. Seems to fit Rosso's profile.
Azul
Abilities: Energy blast (flying crystals, according to the Wiki), shockwave, metamorphosis, invulnerability, regeneration?
Notes: I considered adding 'insanity' to Azul's list of abilities, but I'm not sure that he qualifies in the same way that Rosso does, asking if he could 'eat' his fellow Tsviets aside. I'm also trying to come up with a reasonable sounding explanation for why his barrier field should immobilise him if it comes into contact with another field of similar potency. And finally on the list of things to figure out is what the limit of Azul's apparent ability to regenerate himself is -- Shelke remarks that Azul's 'death' is 'only a prologue to the true terror', by which I presume she means that death (or severe injury?) is what triggers Azul's transformation. Or perhaps Azul's transformation into Arch Azul is similar to Vincent's transformation into Galian Beast -- it restores health. Which...would not explain why Azul remained 'dead' for some time before he transformed and wreaked havoc on the WRO building. (Edit: Zaz suggests that Azul has to undergo a period of hibernation in order to recover a minimum amount of strength before transformation, which would make sense. However, that does make me wonder if Azul might be another candidate for survival post-DoC.)
Shelke
Abilities: Cloning, superspeed, SND, invulnerability (through materia use)
Notes: On the whole, Shelke's abilities appear to bend the normal rules. Where Weiss, Nero and Rosso create three copies of themselves that have to be destroyed, Shelke can create three times that number, though they only last a few seconds. Her superspeed is far more constant than what's observed in Weiss and Rosso. Unlike the rest of the Tsviets, she has no energy blast ability; I theorise that this is because her body can't handle chanelling and releasing such amounts of energy. Apparently she has a hard enough time trying to keep her energy levels up without pulling some of the tricks that her elders do.
Coming up (hopefully sometime this week): attitudes to death and their job.