I am so sorry to hear what is going on at the mission. Maybe you should take this information to the local authorities in your area and request maybe some undercover work be done to help these people? Maybe even hire a good private investigator for added proof.
It’s good to pray and God answers prayers, but sometimes he wants us to be instruments of his will as well when we happen along the way and have the power to do so just like the Good Samaritan in the Scriptures. He did whatever he could to help that poor man who was robbed and nursed him back to health. Maybe you and your group could do the same for these people as they are being mentally and physically abused from what you have told us. While you are working on helping them behind the scenes, keep doing what you have been doing to help them. It does strengthen them more than you know.
Please pray for God’s guidance on how the best way the authorities could handle this problem in your area. Do much investigating, prayer, reading your Bible, and then finally act on it if at all possible. In the meantime, many of us are standing with you in prayer.