What do I need to do to get custody of my nieces?

This may be kind of long but I feel it needs some backstory. I helped raise 3 of my friends kids from birth until they were taken into DFACS custody a year ago. They are in a non adoptive home, mom is not making any attempts to get them back, dad is in jail on abuse charges towards the kids. I was the one who made the call to have them removed for the second time after mom broke the safety plan and let them have contact with dad. I’ve also made numerous other calls over the last 8 years and nothing was ever done until this last time. 3 days later they were taken by DFACS, mom is currently living in a hotel, drinking daily, has begun using hard drugs, and has even been bragging to people about dealing. The current foster home they are in has 10 kids total, 8 foster and 2 bio. Bio kids have their own rooms and all 8 fosters are in one room together, mixed ages and genders. It’s a large 2nd story “bonus room” which is basically a finished attic at the top of some stairs. The foster mom has been very uncooperative with allowing visits, has cancelled many of them and the kids have told their mom that if they misbehave the foster mom tells them they won’t be allowed to have a visit. They also told her they stay in the bedroom when at home unless they are eating or have to come out for some other reason because the foster mom doesn’t want them to get on her nerves. They have the youngest who is almost 3 sleeping in a pack n play and the other two share a bed. The whole thing just doesn’t sit right with me. I wasn’t in a financial position to take them myself a year ago, but I have worked really hard and even moved away for a better job opportunity and I can afford to support them and my own child now. They are not my biological nieces but they know me as “auntie”, I was the one doing a majority of their care when they were with their parents. I have a deep established connection with them, and I want to move forward on trying to have them placed in my home and hopefully adopt them. Mom seems to be in agreement with it, but I don’t know how dad will feel. He has not been convicted yet and to be honest they don’t have much evidence other than the words of the oldest who is almost 6. But he is also a paranoid schizophrenic, who has delusions where he thinks people are poisoning him. The house they used to live in had all the windows boarded up, he would nail 2x4s across the doors at night so no one could get in or out, even put a padlock on it at one point. What can I do? Where do I start? I don’t think either one of them needs to have them. Any advice is welcome even if it’s something I might not want to hear. I can’t just not fight for them. They are as much mine in my heart as my bio daughter is but I don’t know if they will even be willing to give them to me when they have been with the foster parents almost a year with this mostly recent placement.