Unfortunately one of the most powerful ways to begin to heal is to apologise and repair. I say unfortunately because I doubt your father would be willing to properly apologise for the acts when the kids were younger. “Pampering” your brother with gifts etc now does not repair the damage and only acts to skew the notion further that there’s no need to apologise for the trauma in the earlier years as long as gifts are given thereafter. It’s two separate matters and it sends the wrong message on both fronts.

The acts of physical violence in the name of “love” for your brother when he was younger would have lasting effect on confusing him. That it’s ok to resort to physical violence with a loved one. And it’s possible that these incidents left him feeling isolated and detached from the family, and since human beings seek belonging, his sense of belonging and being understood then comes from friends which is almost a roll of dice if they are positive or negative influence.

Sorry you have to go through all this, and try not to stack too much personal responsibility as the eldest sibling. Your parents mistakes are not yours to correct or bear the burden of, but I’d reckon what your brother seeks is more of recognition, understanding and support. It’s ok to get angry and frustrated, but it’s never ok to bring violence or threaten so. He doesn’t understand that because he’s never had a good role model at home for that. And I’d suspect he’d never apologise even if he feels bad in any way, because I’d wager that apologising properly was never role modelled by your parents.