Filing for Custody (Non Parent)

Hi,

My husband and I are thinking about filing for custody of our niece, her mother is mentally unfit, has lost custody of 3 of her 4 kids, she hangs out with drug users who are consistently going to jail after hanging out with her and multiple have been caught with hardcore drugs, she has no job, she does not consistently see her 3 kids she lost, has a pending DUI and felony, and could be on bad drugs herself. Do you think we have a case? BTW there is no listed father on the child's birth certificate that we know of and we are unsure of who the father is but have a guess.