London Broncos second-rower George Griffin will join older brothers Darrell and Josh at Salford in 2015.
The 22-year-old, part of the Broncos side that were relegated from Super League on Sunday, has signed a one-year deal with the Red Devils.
Josh Griffin, 24, recently joined on a short-term contract from Batley and has agreed a new two-year deal.
Greg Johnson, Adam Walne and Jordan Walne have all extended their stays until the end of the 2017 season.
Winger Johnson, 24, has scored six tries in 14 Super League appearances this term after joining from Batley.
Adam Walne, 23, and younger brother Jordan, 21, both prop forwards, are products of Salford's youth system.
"We are developing a tough, young core of players at Salford that are going to make an exciting future for this club," head coach Iestyn Harris told the club website.