How can I adopt a former foster child..we still take the child every weekend and sometimes longer?

We fostered a little two month old boy for 7 months. The birthmom had lost her 3 other children but the judge offered her concurrent planning. She passed her six month probation and was given full custody of her little boy. A few months after receiving custody the mom and dad returned to drugs. Her mother cares for the little boy fulltime but is not in any condition to care for him. Because we are the "god parents" she wants us to take him perm. but cannot get her daughter to meet with us to discuss. CPS won't get involved because grandma is taking care of him. Do I have any options?