Risking the fact that the National Satellite Defense Ministry might trace him, Tristan helped Stefan to get more information as he could. He didn't bother browsing the confidential information that the nation has. If they catch him, he can just wiggle his way to apply as their employee but as long as no one can track him, he will be fine.
Even if he's the number one hacker in the world, that didn't mean he can't be traced. If all those intelligent brains worked together, they'd probably trace him in a month. Well, probably.
Stefan can't act on his own in this matter now that he knew Cayenne was in the hands of her maternal relatives. Of course, he will do anything to get her back but he can't be reckless. For now, she might be safe and sound but if something goes wrong, the Rule family might dispose her. Stefan didn't want that to happen.