1. What did Regulus look like?
I always pictured Regulus as an almost mirror of his older brother, simply because there weren't a lot of genes there to make them look different. Both Orion and Walburga were Blacks by blood, not just by marriage, and so it makes sense that their children would look a lot alike. However, I do think that they had differences in form. I think that Sirius was on the tall side, whereas Regulus was probably a bit shorted. Sirius was leaner, and Regulus was more stout. Not chunky, but stout. Like a scotsman, sort of. I think that Regulus' eyes were shaped differently, too. I always pictured Sirius with wide, bright eyes, and Regulus with thinner eyes, that weren't really bright, but deep.
2. What was Regulus’ personality like?
I think that Regulus started off the typical little brother, worshiping Sirius and trying to be just like him. But then, Sirius started getting in trouble with their parents for not following their wishes, and Regulus decided that he didn't want to get in trouble, so he completely changed over, from being the annoying copycat little brother to the shining example of what his parents wanted. It went from being 'Regulus don't follow your brother's bad example' to 'why can't Sirius be more like Regulus.' I do think that he was probably ignored a bit as a child, so when Sirius started getting ignored, he jumped in there to become the favorite son.
3. How did Regulus feel about his family and their values?
He probably didn't really have an opinion per say, more like it was how he was raised, so that's how it was. It's like in my family, we're raised so that the teens can drink with the adults once they turn 16, and we don't really have an opinion about it. We don't think it's right or wrong, that's just how it is. Of course, he probably started to sort of take on their opinion that anyone who wasn't pureblood was filth eventually, simply because that's what he was around and that's what his friends were like. I'm thinking he didn't see it to the extent that his family did, but went with it because it was easy. And when he joined the DE, it was him trying to take the place of favorite son. Of course, he had to have some compassion, because I'm sorry, but you didn't leave the DE because you were scared. You joined because you were scared. You left because you knew what they were doing was wrong and didn't want to do it anymore.
4. Was Regulus the favourite son of Orion and Walburga?
No, but he was trying. Sirius was the eldest, so he was the favorite. I think that after Sirius was disowned, their parents probably got really strict with Regulus, trying to make him into what Sirius was supposed to have been. And he began to do what they said because he wanted them to love him. But I don't think he was ever the favorite.
5. How did Sirius and Regulus feel about each other?
I think that Sirius and Regulus were inseparable until Sirius began to defect from what his parents wanted him to be. When Sirius went to school and was sorted into Gryffindor, he became something to be ashamed of in the family, so Regulus probably started to resent him. After all, he was home with their parents, who were probably talking smack about him. Eventually, Regulus hated Sirius, because he'd once had what Regulus had wanted as a child (being the favorite with their parents) and had thrown it away. But they never really hated each other. They just wanted to. But in the end, they were still brothers. I think that part of the reason Regulus defected from the DE was because he still looked up to Sirius, and when he was given a good reason to follow his brother's example, he did.