I was there 100% of the time, and know nothing ever happened, but somehow, they got the children to back up their allegations. I believe we had a case of parental alienation. CPS believed the allegations even though there was no physical evidence and there was myself and my brother to attest to the fact that nothing could have happened.
We just went to court in April and the judge allowed him to terminate his rights. Even went out of his way to give him joint custody (because of the Virginia Supreme court case that ruled if you don't have custody, you can't terminate rights you don't have) and then allowed him to terminate his rights.
It was the hardest thing he ever had to do, but the way he looked at it, if he was out of the picture, there would be no reason for the grandparents to continue doing what they were doing to the kids.
I wish you luck. It's a long hard road, and the system really sucks. You at least have CPS looking at her like she's crazy, so you have a much better chance than he did.