This custom is practiced in many places across the country. I'm from Henan, and I have a classmate's younger brother. The fortune teller said that he has a tough luck with his parents. Since he was a child, he calls his parents uncle and aunt, but in fact his father is the eldest child. Also a correction, this has nothing to do with Feng Shui. Feng Shui is environmental science. What you said should be related to numerology.