I don't get how Dal Po recognized his brother but his brother didn't recognize him right away
When his brother introduced himself to Ha Myeong/Dal Po, he referred to himself as 'Gi Jae Myeong', which of course, is Ha Myeong's older brother's name. However, Ha Myeong referred to himself as Dal Po, coming across as a completely different person. Since Jae Myeong's last memories of his brother were a small boy who died with his mother thirteen years ago, he probably wasn't thinking about the chance that Dal Po would be Ha Myeong, so he mustn't have even considered it. Hope this helped! :3