About the bank, I never paid attention to those "earn interest" things because they were so small and there are ways to get much more gold than messing around with them. You can rob the bank, very carefully, especially if you have the levitate spell so you can go in through the roof.
Sorry, I don't recall much about Antonia. Maybe if you just report back to the commander that ends the quest. I also recall before the English patch there were some glitches with Antonia. Check your journal entry, sometimes information is there but the alert that your journal has been updated often flashes very quickly, usually when you are busy with something, and it is easy to miss.
EDIT I loaded up one of my old saves to check journal entries. I had one that said: "I am uncomfortable with this murder. I found Antonia dead . . . ." The next journal entry says "The assassin is dead. . . . " and the next is when I reported back and got promoted.
I think there must be some clue (on the body or near it??) that leads you to Antonia's house where you confront an assassin (it is near the thieves guild entrance, near where the knight trainer is.) Hope something here can help you.