Hwanyoung seems to have a twin? So both of them were born on 29th February?

Yes, he has a twin. No, the twins most likely weren't born on Feb 29th, bur rather Hwanyoung being born on Feb 29th but his twin brother born the next day, a few minutes after Hwanyoung was born. This is most likely why they couldn't pinpoint the destiny of the one who was born on March 1st.