Can I adopt my grandchildren because I can’t locate their mother to see if she would be for me doing so like the father or if she would be against it?

I have had legal custody of my grandchildren for almost 2 years now because FCCs and the courts gave me custody due to abuse/neglect/dependency because the parents were using drugs physically violent towards each other and would not comply with case plans drug screens or any other program that was required of them. I have not heard from the mother in almost a year and have recently talked to the father and told him of my interest in adopting them and he stated that would be best for the children. When this entire incident became the mother wrote out a statement stating that she was signing over all her parental rights and custody then notified me that she wrote the statement and when I went to pick the children up she gave me the statement and I took it to the courts to file custody but later found out that FCCs had already asked for custody be with me.