This is part of the Operation Broken Eagle DLC.
If you've noticed a pattern with the last two achievements, this one is no exception. Squad Members are the equivalent of Survivors in this DLC. There are only two that you need to help out. First up is Sunshine, who is located on the prison bus in front of Rhonda's Garage in Ingleton. Second, The Dutch, is found in a meat shop at the southern part of Central City.
Note: All of these achievements in this DLC need to be completed prior to going to the Mayor's Mansion. After that point, you will not be able to obtain these achievements and you will be required to start a new campaign to do so.