Nathan shook his head at Claire, as either of them joining the fight was out of the question. Claire might be able to heal herself, but Nathan certainly couldn't on his own and just because Peter could heal him wasn't a reason to jump into the fray unarmed and unprepared. Not that he didn't want to do so and tear Sam apart, of course, but he did know the difference between 'want to' and 'should do', the latter involving far more sanity than the former.
"Things can still happen to you," he said gruffly to Claire, even as the familiar mental voice communicated the instructions. Even with that plea in Claire's eyes, something that took superhuman levels of control to resist, he still hadn't intended to do anything but what Peter had requested.
We're staying out of it, he sent back at Peter, wanting to remove as much of the peripheral distractions as possible, such as that muted feeling of dread. If it came to it, he would take Claire and go in order to keep the both of them out of the fight, but he thought it likely she would listen to Peter. Not that she wasn't listening to him, but Nathan still recognized that some things from Peter carried a greater weight than they did from him.
And from what he was seeing, it looked as though Sam would soon be retreating. He tightened his grip on his daughter, one hand unconsciously stroking her hair as he waited to see what the end result of this fight would be.