Hi, Thank you for your question and welcome. My name is ***** ***** I will assist you.
I am afraid there is no way you can pursue this course of action without implicating yourself in the fraud. Not only will you be turning a blind eye to Bribery and Corruption but you will also be treading into the realms of blackmail yourself. The only way you could conceivably leverage this is you made A aware of the confidential information you possess without any specified threats or demands for payment and have A come to the realisation by themselves that you posses toxic information. If I were in your position I would just either keep quite (as long as you not in anyway connected to those payments) or blow the whistle. If B was legitimately owed sweat equity from A, he should just explore suing A.
Unfortunately there is no way to escape that the fact make these threats will be construed as unethical and for that reason it is almost certainty not worth associating yourself with such bribery and corruption.
I look forward to hearing from you. Kind regards AJ
P.S my apologies for any typos - this chat service is done in real time.