How to Get Custody of My Granddaughters

My question involves a child custody case from the State of: Missouri
I have two granddaughters ages 7 and 5 that are currently in the legal and physical custody of my son. He obtained full custody after they were removed by child protective services from the care of their mother for manufacturing meth in the home, the home was raided by the DEA and the children were removed and placed in my care while my son went though the steps to gain custody. She went to prison, she has served her sentence but the conditions of her parole is zero contact with the girls for 5 years. Initially, I was happy my son got custody as he lived with a nice girl who seemed willing (at the time) to help him raise the girls. He has had custody for a little over a year and I have seen the girls go downhill dramatically since living with my son and his girlfriend. The older girl has debilitating anxiety attacks and the younger daughter has behavioral problems. The girlfriend is emotional abusive and tells the girls they are bad and liars and how they are ruining her life, the younger girl is having accidents constantly and is humiliated as a result, she will make fun of her until she cries. They are currently living with the girlfriends mother who is just as bad as the girlfriend. Lately, the younger girl has been showing up with bruises, one large one on her foot and she said the girlfriend stomped on her foot because she was in the way and recently, a large bruise on her forehead where she was hit in the head with a toy. Its obvious my son does not want the responsibility of these girls and does nothing to move them out of the girlfriends mothers house or to protect them. They have no bedroom and sleep on the floor in a sewing room, the girlfriends mother is a hoarder and the house is really dirty. The whole situation is unhealthy. They have no stability. I am ready to do anything I can to get them away from them so they can have some sort of normal childhood.

If you believe that the children are being abused, you can report what you know to protective services for investigation.

Why does your son prefer that the children live with his girlfriend's mother over living with you? Why did he say "no" when you asked if you could care for the children?

They are school age; their school should have mandated reporters. Why have the signs of abuse not been reported already?

I suggest that you enlist the services of a family law attorney to help you obtain placement of the girls in the event they are removed from their father's custody.