My sister has baby with her boyfriend she was recently diagnosed with a mental illness. They live in louisiana and i live in ny with my husband
Likely the father has superior right to custody. Your near unique situation suggests you need a consultation with a New York Family Law attorney.
I gather your sister is not already adjudicated as an incompetent adult, your niece lives with her parents and they are located in another State. You may require lawyers in both states, but first try to develop a legal theory for a reason you are entitled to custody of your niece instead of one or both of her parents.
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