Frankly, I would refer all questions as to how his daughter managed to afford a house to her - it is her business not yours to tell her father or anyone else about the transaction.
You are, of course, at liberty to ask your niece not to tell her father that you have helped her out.
You know your brother, and know what kind of nosy questions he may ask'.
My stock answer would be, "I really cannot say." after which I would change the subject.
If that doesn't work, try, " I must rush, something's boiling over in the kitchen!" and disconnect the call.
The media are already after Andy!

