Legal guardian of 14 Month old

What is the name of your state? Texas

We have a friend of the family that has lived with us for several years and we consider him our nanny for our two sons (5 & 7) and pay him for his work.

He has a sister who is in an abusive relationship with drugs and violence involved. He has tried on many occasions to help her get out of the situation, but she refuses. She has a 14 month old son (Biological Father in prison for next 12 years) and a newborn baby girl with her current live-in boyfriend. Her current boyfriend is a little psycho and last week assaulted our Nanny's mother when she was taking the kids for her days off (which she does weekly). This guy physically assaulted her and was arrested - he apparently has a long rap sheet. Our nanny's sister also exhibits signs of physical abuse, and the 14 month old has an unusual amount of scarring, some look like burns. Both the sister and the boyfriend are involved in a drug culture. When the boyfriend assaulted her mom, the sister let our nanny take the 14 month old with him to stay in our house until things get settled.

Our nanny's mother is going to try to get custody of the infant through the courts, and we want to get custody of the older child. We can't see sending this child back into harm's way, when his uncle is one of the few people in his life that truly cares for him. We don't think his sister will agree to give him up permanently, not sure about father in prison. The sister is not a bad person, but picks the bad people to be involved with. The child has been with us for a week and we live a good distance away from the maternal mother, but both in Texas.

Question: What steps do we need to follow through on to get legal guardianship of the older child? Also, what do we need to do/not do to help our case? The grandmother also wants advice on how to go about trying to get custody of the infant. We are prepared to fight for the protection of these children, but fear reprisal from the current psycho boyfriend.

Thanks in advance,
Jimmy