Barton and Colbert were with Kansas City, while Ratley was a sixth-round pick of the Browns last season.
Colbert, 26, is a former seventh-round pick of the 49ers back in 2017. He was in the second year of his four-year, $2.48 million contract when the 49ers placed him on injured reserve coming out of the next preseason.
San Francisco later waived Colbert with an injury settlement and he signed on to the Seahawks’ practice squad in 2019. He bounced on and off Seattle’s practice squad before Miami signed him to their active roster.
The Dolphins re-signed Colbert to a one-year, $1.775 million deal this past March but elected to cut him loose earlier this week.
In 2019, Colbert appeared in six games for the Dolphins and recorded 22 tackles, no interceptions and two passes defended.