Paternity Testing to Eliminate a father

My brother is in the midst of a custody battle for his two daughters (4 1/2 and 3 1/2 in PA). He was in a long term relationship with the mother (10 years) and they also bought a house together. Both daughters have his last name on the birth certificates. She has always held them out, to the world, as being the father. She left last year to live the life she wanted to lead (drinking, drugs and men). My brother immediately filed for legal and primary custody and allowed her visitations (no overnights). She has now filed a petition for DNA testing claiming that neither children are his and when the DNA proves that, he is supposed to relinguish all rights to his daughters. So far, the hearings have not been going his way and we are awaiting trial that will deny or grant this petition for paternity. Any and all insight to our case would be helpful.

P.S. She is tested for drugs and alcohol periodically and has tested positive for alcohol and coke and still the system makes my brother hand his daughters over to her for visitations. She is even allowed make-up visits for missed days due to her scheduling problem. She has named the two fathers in her deposition but has no plans of alerting these men that they are the fathers. One is a coke dealer and one is in jail. Her family has a history of incarceration, drugs and alcohol. Her parents are supposed to be with her as supervisors during her visitations, however they leave.