Custody of a Child previously in CPS care

[nater1977]

My fiance's grandson was taken into CPS custody 2 years ago after an accident with his sitter. It was found that the sitter abused him but CPS wanted to investigate my fiance and her family also. She was angry and not real cooperative at first. She never had received legal guardianship from her daughter but also was never found unfit by CPS. The grandson was place with my fiance's mother his great grandmother. We have recently found she is verbally abusive to him, he is only 3 and gets called a**hole and b@$tard. We would like to file custody but want to know what real chance we have of winning. We have a 3 bedroom house in a middle class neighborhood. Both have stable job history with decent salaries. Her mother has been diagnosed bi-polar. But does have the CPS placement on her side and a 4 bedroom house of her home. Wouldn't a grandmother's rights out weigh a great grandmother's? And is there any way we would be allowed to bring up her illness?