Peter held onto his niece, stroking her hair and trying for all he was worth to let his own (relative) peace and calm guide her. Gradually, he felt her sobs slowing, felt the acceptance beginning to settle into her mind. He didn't loosen his hold.
Nor did he intrude upon Nathan's solitude, merely leaving that gentle sense of presence in his brother's mind. With it was a sense of comfort; it helped him to remain calm, and be the strong one for Claire, to have Nathan there.
When Claire was steady enough to raise her inquiry, Peter waited a moment before answering. His policy with Claire was honesty, always honesty, but some things were a little too hard to speak of just yet. Such as her impending fate.
No. He would find a way to prevent that. No matter what, he would find a way.
"He's here," Peter answered. "Hiro... Hiro's a time traveler. He's been trying to find a way to change things for the last five years. To stop the bomb. He did it, Claire. He changed it. And there's a timeline where it never happened. Where New York didn't explode. That's where Nathan is from. Nathan... And Heidi. Simon and Monty. They're here. They're all here."