I think that the problem may start even earlier. I suspect the prime age for kids becoming functioning, contributing members of the community is the years from about 13 to 16.
Kids that age desperately want autonomy, independence, but also want to matter, to do "real" things.School can help but in many cases it doesn't feel real, and the kids don't have much independence there. Things like jobs in the early teens are increasingly rare, people don't want to hire them as babysitters. A lot of parents are not even keen on leaving kids that age to walk home alone, or stay home alone.
Post about 16 years old they have found other ways to occupy their time, gaming in particular fulfills the need for dopamine response, or social media for girls, and they have become used to not contributing to society. Some will learn it later, but even there I wonder if they are ever as productive as they would have been otherwise.
YYY @MangyInseam
This isn't something that happens overnight.
Infantilising young teens leads to failure to develop, socially, psychologically and emotionally.
In the case of the OP's brother, the mother needs to press charges for violence, and change the locks. The brother is not experiencing any consequences for his choices.