ESPN and The Milwaukee Journal-Sentinel reported Brook, a former All-Star, will sign a four-year, $52 million contract to stay with the Bucks. Robin will sign a two-year, $4.8 million contract, according to The Athletic and Yahoo! Sports.
The brothers previously were teammates at Stanford University in 2007. Brook and Robin were each first-round selections in the 2008 NBA Draft.
Brook averaged a career-low 12.5 points in 81 games for the Bucks last season, but made a career-high 36 percent of his three-point shots. He averaged 11.2 points and 4.7 rebounds in 15 playoff games.
Robin averaged 9.5 points and 3.9 rebounds in 74 games (36 starts) with the rebuilding Bulls.
Neither brother has hinted about their possible living arrangements. The two considered rooming together in 2015 when Brook was with the Brooklyn Nets and Robin was in his only season with the rival Knicks, but they decided against it because of their cats.
"The cats really wouldn't get along," Brook told The New York Post that year. "They just wouldn't allow it."