Thank you to everyone who has been sending good thoughts. Thankfully things have turned out okay - it is still a crummy situation but we're able to relax for now.
My dad talked to Bobby, Sheena and Taylor. They are all fine and safe - Sheena & Bobby's side of the story is that when Sheena's parents found out about the heroin they lost it and started a fight and kicked them out. Sheena refused to leave without Taylor, and Taylor didn't want her mother to go without her either. Bobby had enough of the fighting and took Tay to the car & Sheena then went with them. They wanted to bring Tay here, but in the heat of the moment they ended up just leaving to go wherever it is they are now. (Dad didn't mention where they are exactly.)
Sheena and Bobby both want to go into rehab and were looking this morning for someplace they can go - but all the centers are closed for the holiday weekend and the earliest they'll be able to get in is Monday.
Sheena said she hoped nobody called CYS, which dad told her the truth that we did call them because her mother said to & that was the advice of all the police and other folks we talked to about the matter. With everything her mother was saying we were all worried sick but as it turns out her mother is a drama queen. I'm frustrated with her that she put us all through this - but it is what it is. But at least Sheena knows CYS was informed and that she can expect they'll be investigating; she isn't too upset over it, she knows it was done out of concern for Taylor and that we were all worried sick because of everything we were told by her mother.
So, we've all heaved a sigh of relief. There is still a lot to deal with because of all this, and it's going to be a long road. But at least for now we know that everyone involved is ok and safe. Niece may well end up staying here on an extended visit, or maybe my brother will finally be able to get custody. Who knows. But the main thing is she is safe, and we'll be getting to see her again soon.