How did Clementine and Zbaltazar survived the sewer in the first place? They obviously had gone through the sewer and it was infested by Zurks (since Zbaltazar managed to warn Momo about it) but they didn't have weapon back then. So how do they survive? Are they gone through other routes we are not seeing in game?
It's not clear how long ago they passed through, so it's possible the Zurk infestation was significantly less severe at the time.
It is possible they didn't go through unscathed. A WMG stated Zbaltazar got injured in the sewer and Clementine had to leave him behind in Antvillage.
They may also have been able to access non-infested shortcuts that the cat couldn't. Companions, unlike Zurks or cats, can open doors manually.
The Snitch
Who paid Blazer to give information to sentinel? Does sentinel even understand the concept of money? Who put the Clementine's wanted poster?
The robots inherited a lot of social constructs from humanity, apparently including money. If "Wanted" posters with cash rewards were used during the riots prior to the plague, the robots and sentinels would have something to copy.
B-12 and the Cat (Nobody else).
Why does B-12 never talk to (or have his existence acknowledged by, for that matter) any of the robots himself? He's clearly his own individual, you'd think he'd want someone to talk to after so long on his own, yet none of the robots even seem to acknowledge that he even exists.
It could be a case of Heroic Mime, in which B12 (or the cat, translated by B12) actually spoke to Companions but we weren't shown what they say. However I am inclined to think B12 PURPOSEFULLY said nothing to them and acted like a mindless drone based on Doc's dialogue (he only referred to B12 as cat's drone and didn't address him directly). For what reason, we can only guess. Maybe he wanted to observe how far the Companion evolved and didn't want to directly interfered with them?
Another option is simpler: they might just be shy. It is a well observed phenomenon that shy and/or introverted people tend to feel much more comfortable and open with their pets than with other people, and the cat might have triggered the same in them, in spite of their obvious intelligence.
It can be because they're not aware B-12 can understand them. If you think about it, the companions don't really see B-12 as the same as them, and probably haven't seen a drone like him before in years. Only Doc seems to recognize him as a drone, and even the sentinels put him aside the other robots when he's in jail. B-12 also looks somehow similar to the sentinels, meaning that some companions might believe him to have the same sentience as one. If he also has a similar hardware it could mean he doesn't actually have the capacity to answer back to any of the companions, yet he can understand them. If the hardware was programed to be used for humans and animals, it wouldn't be strange if they didn't consider communicating with companions on its programming.
Neither B-12, the companions, or the cat share a common language (programming) between the three of them. B-12 isn't a robot per se, and thus lacks the capacity to talk with and/or like one, they can talk with the cat however. It also seems like the vest enables the cat to understand the companions, considering we only understand Clementine when we're wearing the vest. By that logic: the cat understands B-12, and understands the companions when is wearing the vest, but neither Clementine nor B-12 are able to understand each other, and the cat cannot translate for them cause it is a cat.
The cat and B-12 speaks English while robots speak robot language, it can be translated to English but has a different alphabet.
By all appearances, the Sentinel drones can't talk, so it's likely that Companions assume B-12 can only relay the cat's messages rather than speak for himself.
