What do you think might happen. Need advise and kinda a rant.

The father's bio family have almost no chance; the child is an American citizen with the rights of an American citizen and it is very unlikely the child would be placed with them unless they live in the USA. If the father is involved in a current CPS case in which children were removed from his partner because he is violent (or even if that case is closed), I doubt very highly CPS would leave his child in his care. And could he be relied upon to draw boundaries with the mom? Certainly you should make yourself available as a permanency resource. Would mom be willing to give you custody, if not sign a surrender? If she has a history of long periods of sobriety, it may be that she can get into a program and have the baby placed with her there after a (relatively) short time, and that may to everyone's benefit. Whether that is close by you (I assume mom's family of origin is where you are? and could be a support for her?), or where she is currently living will probably depend on both her preference, where rehab is available (or whatever services she needs/is required to use), and if the counties will cooperate. If it's a state case, they should be able to transfer it pretty easily. Even if mom moves by you, I don't know that I would volunteer to foster until it was pretty clear what the plan is. If it looks like she could RU quickly (if she cleans up and stays clean, as you say she is capable of doing), you should probably steer clear, but let everyone know you are a resource for permanency. It doesn't seem worth the psychological risk to your kiddos to foster a sibling who might go away after a short or (worse) long while. Sounds super complex; I hope you all find a peaceful way through it.