Well, he'd like to call her 'Mom'. But he could sense she wasn't totally comfortable with that. And if she was right about what she was saying, then it wasn't accurate, either. (And he'd never known his mother to lie, especially not to him or his siblings, so he trusted every word she said. No version of Leia could be dishonest, right?)
"So, the Han Solo here--" Jacen held up his PADD to indicate where he got his info. "--he is my father? And knows about Jaina and Anakin? But you..."
He paused, biting his lip. So. Ben wasn't his tiny baby cousin, to this Leia. Ben was a brother. He decided not to mention that discrepancy for as long as possible.