What are Lesbian parents custody laws in the US if not the Biological parent but signed the birth certificate as the other parent?

It depends entirely on which state they live in - the federal government generally stays out of family law, and leaves it to the states. As such, each state has its own laws related to child custody.

So, if you're in a state that allows for adoption by same-sex couples, and allows both partners to be listed as legal parents, the legal rights with respect to child custody should be exactly the same as a heterosexual married couple who are the biological parents of the child.