Legal Custody, now what?

Hi all, I haven't read through all the threads but I'll be looking for more information in those after I post. Quick history: Today my husband and I took custody of a cousin's baby. The baby has been with us for the last month and a half, and with grandparents 5 months prior. Mom was able to take care of baby for the first 2 1/2 months before her addiction grabbed a hold again her child was removed from her care. The little guy we have is number six for this mom, and as of today she has custody of none of them. Five of the children have been placed with family who have legal custody, (2 with maternal gp, 2 paternal gp, and one with us) and one child was adopted out at birth due to addiction. Mom has been in hiding for the last 5 months due to a warrant for her arrest. When mom is found she will be going to prison due to a felony conviction 3 years ago that she didn't obey court orders on. Because of mom's hiding she has not seen the baby since probably February. Now my questions... We want to adopt this child. We love him so very much and our bio kiddos do as well. We know that the chances of mom visiting, paying support etc. are very slim due to her addiction, and now prison time she is facing. Does anyone know the rules on an adoption like this? I know there is some kind of 90 day abandonment claim we can do. However, since she has custody of none of her children would that also help us in this case? Also do relatives have to also wait the six months before the child will be placed with you? Finally anyone know when the 90 days starts? Mom has not been at any of the hearings over the course of this. Mom has also not called to check on the baby since I have had him. Any input would be greatly appreciated. We will be talking to an attorney, but wanted to see if some of you could help share your experiences. Thanks! Mommaof5