The 33-year-old Boulton had eight points and a team-leading 113 penalty minutes in 62 games last season. He became the franchise's leader in penalty minutes on March 20 against Philadelphia.
Terms of Boulton's deal were not released.
The 27-year-old Ross, a native of Huntsville, Ala., appeared in three regular-season and three playoff games with Philadelphia.
The 27-year old Sifers played in 14 games with Minnesota and spent most of the season with AHL Houston.