Analogies seem to be failing. So lets actually talk about the case then.
Cambridge Analytica asked user A for permission. Facebook allowed CA to gather information about B (A's friend), and B NEVER provided consent. B now is wondering who to sue: Facebook or CA.
My opinion: (IANAL). B sues Facebook. Then, Facebook sues CA.
This leads to a few results:
1. If B loses its case against Facebook, the game is over.
2. If B wins its case against Facebook, Facebook continues and sues CA.
3. If Facebook loses vs CA, then the game is over and Facebook is found to be at fault. If Facebook wins vs CA, then CA was at fault.
4. If CA was at fault, then maybe CA will then sue its consultant over the issue, and it may continue. So on and so forth until the root cause is discovered, wherein the game ends.
Simple process. At least... simple if everyone could afford the proper legal process. B probably can't afford it and many "Bs" need to gather together for a class action lawsuit and all that jazz.
The hardest part of the puzzle is what exactly B would be suing over. It feels like B was damaged as a whole, since Facebook leaked B's information to CA. But its hard for me to formalize the complaint. Then again: that's a lawyer's job to find out.