Fostering niece

Our niece is in the nicu addicted to drugs. Mother was doing heroin and who knows what other drugs! Baby is going to us when she’s out of hospital and we will be her relative caregivers. Both parents are addicts. One is a felon and the other has a warrant out. Neither has custody of their other children. The mother has a 6 year old that we are pretty sure the grandmother has guardianship of. That baby was removed after birth as well for similar reasons. We would adopt our niece if parents don’t do what they are supposed to. Which we don’t think they are capable of taking care of a baby they don’t work and live with my husbands mom for free. So I guess my only question is, how long do they have to get sober and get her back? Or how many chances do they get? My fear is them getting sober for a month and then going back to drugs. Then off drugs and back and forth. What happens then?? At what point is it no more. Because I see them trying to get off drugs but then going right back to them. Any advice or similar stories would be helpful