Emergency Custody Please Help

[PanickedGrandmother]

My grandson's father has custody of him.  My grandsons resides with his father and his wife.  My grandson's father has a checkered past that includes several arrests, felony conviction, and a decade long history of opioid abuse.  He was arrested twice this past week and is probably looking at a very long sentence.  How can his mother go about getting custody returned to her?  The child is now living in his father's home with the step mother.