My sister was diagnosed with ALS and has custody of my nephew. The child's mother does not want him and I am wondering what my husband and I need to do to take custody or adopt him.

She has a court order awarding her custody? What state or country is that?

She has leagal custody through the state of South Carolina. She moved to Oklahoma last month before she got the diognosis.

Your sister has custody of your nephew because the mother doesn't want him. Who is your sister to the mother? I'm assuming the mother is either the sister or sister-in-law of you both. Where is the father in all this?

But the bottom line, is you need to go to court to obtain custody or to adopt. The father will probably need to be contacted (or at least attempt to contact) for his approval.