Anyways, I have doubts this is worth your time (and money) regardless of your answer to my question above.
If you're looking to RE these mobile apps solely for inspiration, you're better off hiring senior-level employees with experience working for banks and/or in fintech and starting from there. If you insist on RE-ing something, then try to RE a fintech product that you are trying to emulate.
Alternatively, if you're telling me that you guys plan on somehow piggy-backing off of the banks' APIs, then you need to work directly with the banks. If that's not an option, then your product has already failed and it's time to move on.