It sounds like your brother has made his ambitions and decision to end contact with the family crystal clear.
He is not seeking his relatives approval or feedback.
Nor is he attempting to persuade any members of the household he grew up in to agree with his opinions and ambitions.
He is focused on his career and building the future life that he wants.
It's time for his relatives to move forward and focus on building themselves a happy future.
Your brother has bravely chosen to fulfil a very sensitive police career role.
One where he does his utmost to assist the counter-terrorism efforts of international law enforcement agencies, uk intelligence services, uk criminal courts and uk armed forces in seeking to keep the uk & its mainstream population safe. from all manner of predators.
Both domestic and international.
Your brother wants to help the uk.
Thus he has chosen to commit to a career supporting the nation's efforts to protect both uk public order and uk national security.
From all sorts of criminal sewage, troublesome militants, fanatical cranks, sinister cultists and other rotten apples that constitute a serious threat to the uk or its closest allies.
Your brother understands the risks of his job having undergone extensive professional training and in-depth vetting.
He is aware of all the most forseeable consequences that come with his choice.
Your brother won't change his mind because his parents and other relatives he used to live with disagree with his decision.
The UK is fortunate to have so many dedicated and highly skilled patriotic citizens like your brother.