need some help!!

im looking for any information that would help me adopt my nephew. please have patience im soo very new to all of this. my sister in law is a drug addict living on the streets. she had a baby boy 1 year ago and after a "month" of post birth recovery while the baby was in the hospital detoxing from heroin and methamphetamine he finally came home. and when i say home i mean grandpa and grandmas house where the mother was staying at the time. the mother abandoned him after a week of dealing with him. she and the supposed father is now back on the streets still doing drugs and its coming up on 1 yeah that they havent tried to reach out to see her son, be apart of his life etc. my wife and I have been raising this amazing boy with a lot of help from Grandma and Grandpa he is doing great and becoming a cool little human with personality ! now is what im struggling with is the adoption part.. we have discussed doing it and are both ready and willing but the mother is the problem. how can we fight for this defenseless boy from a crazy drug addicted 35 year old child? we count every day as a blessing buy know that at any moment she can come in and take him away and we cant stop her. are there any resources in california for this ? is there a way we can adopt him and keep custody the whole time? am i even in the right place for these question!!? please any help will be sooo appreciated