Concern/Question about loss of custody

My brother and his wife recently gained custody of their two grandchildren. The mother (their daughter) lost custody after someone reported her to CPS for drug use and possibly using drugs in front of the kids. She was given the opportunity to go to rehab but afterwards she continued to fail drug tests. During the time my brother and his wife were gaining custody, they were told the mother is not allowed to live at the residence with the children.

Fast forward a few months and she is living at the house with them. I'm concerned for the kids (that have been through ALOT) and it would devastate them to be taken away from their grandparents. Could my brother lose custody of the kids since he is allowing their mother to live there? She may or may not be still using meth.