If your wife and you have sole custody, there should not be a problem. If the biological father had parenting time, he could object to relocation to another state. Given the fact that he is not involved in the decision-making and does not have any court-ordered parenting time with your step daughter, he should not have any basis to file an objection to the move. Yes, grandparents have rights to grandparent visitation if they decide to pursue such visitation right. However, that is assuming that they file for grandparent visitation and the Court deems that they should be entitled to such rights. It would be best for you to work out an agreement with the paternal grandparents for visitation of their granddaughter so that it does not come to that.
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.
You have a difficult situation. Based on your comments, there are no orders for parental responsibilities (decision making and parenting time). With no orders, you would not be disobeying an order if you move out of state. However, the new state will not have jurisdiction to do anything until you have resided there for 6 months. In the first six months after your move, the father or the grandparents could file an action seeking certain rights and you would be forced to return to Colorado to litigate whatever issues are raised. It would be best to talk this situation over with an experienced family law attorney before you do anything.
If the biological father's parental rights have not actually been terminated then there is much that he could do if he chose to. He could seek a court order for parenting time and could oppose the relocation. However, doing so would require him to actually get involved in a court case and would doubtless result in a child support obligation.
Without the active assistance of their son, there is nothing the grandparents can do. They cannot initiate a case to seek grandparent visitation if there is no custody case filed by the father.
You can reach Harkess & Salter LLC by phone or email. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.
Just to supplement the answers of the other attorneys who have responded, if there have never been any court orders entered, then your wife does not have "sole custody" of her daughter, and, unless the child's father's parental rights are terminated and you adopt the child, you will never have any legal rights, sole or otherwise, with respect to the child. Where, as here, there are no court orders, the father has exactly the same legal rights with respect to the child as does the mother.
www.karlgeil.com. This answer is provided as general information about a legal issue, is not legal advice specific to a particular case, and does not create a lawyer-client relationship with the person asking the question.