This may sound simplistic - especially in light of the gravity of the situation - but things tend to work out.
They just do.
I also would, in a heartbeat, raise my grandson if his parents relapsed. Another relative of mine took her daughter's first born. The girl was 15, drug addicted and her lifestyle was awful. Then at age 20, she got pregnant again... this time, the mom could not take another baby, and the "baby daddy's mama" decided to go for custody.
Since the baby daddy and the girl were split up (he was in prison); this terrified her. This second baby would NOT be available anytime she got clean and sober.
So she got sober and fought for custody of the second baby. Then she regained custody of the first baby.
What I am saying is the first one being raised by grandma was exactly what needed to happen. The second one going to a perfect stranger is what she NEEDED in order to get clean and sober.
Only a power greater than me could ever know which is the right answer.
The longer I am in program, the more I am able to let go and let my Higher Power run the show... He has some interesting solutions!
I am glad you are there for that baby. He is getting unconditional love... we can all use some of that.
((hugs))