Again, more of what is wrong with our society that you would even pose the question.
Even pre-assinine regulation of the banking system, no legitimate bank would fund a known terrorist organization. While I am not completely versed in civil law, in the criminal courts, the airlines would have to prove something like mens rea meaning 'guilty mind' (or that the banks knowingly funded such terror groups, which they would not do).
That said, I would be amazed to see either airline dish up ANYTHING related to 9/11. If I am not mistaken even the insurance settlements on the A/C are kept non-disclosed and the airlines want it that way. To dredge up ANY news of their airline being involved in the attacks would go against everything their PR
departments have done to mitigate the airline involvement.
(and that is a huge if) the banks knew of terrorist ties to those being funded and circumvented all of their own regulations in reporting (including their independent audit departments), then yes, I would say they 'could' be liable, but neither airline would even fathom such suit considering whatever meager punitive damages they could receive would be greatly outweighed by the legal fees to do so and only stir up bad PR
By reading the above post you waive all rights to be offended. If you do not like what you read, forget it.