they saw their graves and realised that they were copies and not humans.
they realised that the humans killed them.
nibs saying she was pregnant was a sign of wanting to be human (even though not)
wendy was betrayed by her brother.
xeno is influencing wendy.
synth tech does not work and they all go crazy eventually (which is why there are none in the future)
...
Lots of stupid logic from the show on this, though.
First of all, the company would've neverrrr made graves for them. One of the dumbest parts of the entire show. There's an existential and philosophical argument that they aren't even dead. Second of all, they were all terminally ill, and they were all about to be dead anyways. So how the fukk were they killed by the humans? They weren't. The only reason they're in any form of conscious existence is because of Prodigy/Boy Kav.
Now, this "are they dead/were they killed" is something the show could've actually spent time wrestling with the philosophy of, and they could've made this interesting, but they just went "derp, gravestones = they murdered us, so let's kill them all."
That's such a generic and dumbed down way to write this conflict. And how was Wendy betrayed by her brother? Because he tasered Nibs for 15 seconds after she ripped off that security guard's jaw? Lol. Nibs was totally fine right at the beginning of the next episode. And why are ALL the kids on board with mass murder all of a sudden? Again, these are all 10-12 year old kids.
I do agree that the Xeno may be influencing Wendy a little bit, but that's way too generic and rushed, and not fleshed out yet to be believable for her to go full heel turn so fast. At this point, Wendy went from a terminally ill, sweet 12 year old girl, to full mass murdering psycho in just 1-2 episodes, and it's just super rushed and pushed the suspense of disbelief.