Federal prosecutors contended 40-year-old Henry Ruffin of Williamstown and his 42-year-old brother, Ronnie, of Lindenwold, threatened their 20-year-old nephew because they feared he was talking with authorities.
Defense lawyers, though, claimed the brothers were only trying to "straighten out" their nephew, who also faces charges in the case.
Citing both defendants extensive criminal records, U.S. District Judge Joel Schneider denied them bail on Friday.
The brothers are among six people charged in the death of 20-year-old Nadirah Ruffin, who was taken at gunpoint by robbers in March. Her body was found in the Schuylkill River in Philadelphia nearly a month later.