About the pro-Roman and anti-Roman, in every tribe there were "parties" divided. For example Dumnorix and Divitiacos.
The Allobroges it is possible that they were "controlled" due to their territory sharing border with the expanding republic. I remember that around 63 BC they complained for maladministration.
The Arverni saw their "kingdom" and alliances fall apart, having a pro-Roman oligarchy maybe was enough to keep the divide et impera...
For the invasion during the principate, the situation was quite similar: Caratacos expanded against the Atrebates/Cassivelaunos against the Trinovantes; same "High King" authority.