Vainuku and Coleman are being brought in to compete for the starting job at fullback, the Falcons said in a release.
Coleman was signed by Seattle in December of 2012 and played in 31 games with seven starts for the Seahawks. He has 11 career receptions for 91 yards with two receiving touchdowns. He also had 10 carries for 35 yards.
Thornton was selected by the Indianapolis Colts in the third round of the 2013 draft out of Illinois. He played in 37 games for the Colts, with 32 starts, playing both left and right guard.
Vainuku was signed by the Houston Texans in 2016 out of the USC, but was waived/injured in September.