How are my parents able to get custody of my daughter if something were to happen to me?

I am looking to speak with an attorney regarding some questions I have about my daughters father giving up his parental rights. He left us about 8 months ago & has had very minimal contact since. I do not get child support because he is a felon & does not have a job. My mother & father are my daughters secondary primary caregivers, they care for her at their house while I work fulltime. I am concerned that if anything were to happen to me, the father would automatically get full custody even though he does not have the means to financially or emotionally support her, he does not even have a home. I would like my parents to get custody of her if something were to happen to me because he is not fit to be a father. I have read many articles about Grandparents rights & understand we would have to go to court & a judge would make the decision. My daughters father would most likely voluntarily give up his rights to benefit our daughter. I am just looking for some guidance on where to start