If you have phone contact details for the hiring manager, give them a call. Tell them exactly what you've put in this message, ending with "I don't know if it's an issue or not for you, but wanted to make sure that you're aware".
It may not be a problem - in which case, they'll let you know, and will appreciate the fact that you were proactive. If it is a problem then it will still be a problem when you start at the company, only then, they have to work out what to do, with no advance notice.
I can't see a downside in being upfront about this with them.
Long story short- I applied for my dream job a month ago and I have been progressing in the interview process. My future step-mom (will be official in September) unannounced to me had applied at the same company, but for a different position in the same department. It is my understanding that I would never report to her, or visa versa. She was further along in the process when I first applied (her job was posted earlier) and just accepted a position today.
I have a 3rd interview (my first in person) this Friday, and I don't know how to bring up this positional conflict of interest to the hiring manager. I know I need to mention something before the interview, but don't know if I should call or email. Not to mention I have no clue what to say when I decide a mode of communication.
This is my dream job so I am hoping to find a way for both of us to work there without it being an issue.
Note- The company does have more than one office so maybe if we worked in different offices it could work.