What are the chances?

My husband and I have in our care 2 beautiful babies- almost 17 month boy and 2 month old girl. They were taken the day the baby girl was born due to drugs and child endangerment. There is also domestic violence in the mix. The little boy was already taken from them, in the past. Bio dads mom is in the picture. The bio parents are wanting grandma to be assessed. It seems to me that bio parents know the probability of them getting their kids back is slim or else they would not want grandma assessed. I know that grandma would need the background, housing/ financial, physical, etc. done to get babies. With the background of the bio parents, what is the probability that the court would give grandma guardianship of these babies?