Remus had decided to give Sirius and Harry space to get to know each other. From what others had said, Harry had bonded with the older version of Sirius he'd known and Sirius...well, it was James' son. Probably didn't need to spell it out past that. Remus had only known Harry as a baby and doubted he, himself, was anything like what a version of himself ten years older and a professor would be like. So, he'd get his opportunity to get to know this adult Harry as time went on and let Sirius have the time. It would be a balm, maybe, after learning of Prongs' death.
So he wasn't difficult to approach, on his own, keeping watch and whittling at the small statuette he'd started the other day.
Regulus' approach wasn't exactly what Remus was expecting.
"I'm sorry." Remus paused in his whittling. "Someone told you I'm a werewolf, that there's a potion that can help, and you're reaction is to...come talk to me like a normal person and offer to help?" If Remus sounded astounded, well...he was! First of all, he wasn't sure he wanted to know how Tonks knew he was a werewolf. Second, he wasn't at all certain they needed to discuss it out in the open, even if no one was paying them any attention. Third...people didn't do that. Not in Remus' experience. His friends had been the exception to prove the rule. So, to have Sirius' younger brother, someone with whom he'd never particularly gotten along, come up with offers of aid instead of accusations was surprising to say the least.
Most importantly...did everyone know? Was he going to have to see what the castle did if he left? Even if Regulus Black was as crazy as his brother, walking toward the werewolf instead of running away, Remus doubted that was a general feeling shared by all.