When Yvette refuses Nick's marriage proposal, she puts her right hand on his face. When the angle changes she suddenly has both hands on his face.
Nick Kegan does appear to be a bit young to be a brother of a U.S. President who was slain nearly 20 years earlier. However, it's explained that Pa Kegan fathered them from two different wives. Men are known for fathering children (from different women) decades apart.