My fiance's son was born while he was incarcerated. The child was taken from the biological mother and placed in foster care. The foster mother was trying to adopt the child but my fiance's mother which is the child's grandmother fought for custody and adopted her grandchild. I wanted to know can she place the biological father (her son) on child support and if she does would she have to put the biological mother on child support too?

If the child was adopted rather than the grandmother receiving custody---then no. But your fiancé should have documentation given to him that his rights were terminated.

If the child was NOT legally adopted, you bet she can go for child support from both the mother and the father. And if she is on any government support at all, the STATE will go after both parents for child support.