Fighting for custody?

im 20 and in the military im married. im going to be going to court to fight for custody of my niece my sister ped away in march and she left behind this 19 month old lil gurl. ive never been in a custody battle b4. it is between me and her fahter. hes 19 doesnt have a job doesnt have steady income. but he is dating a parole officer who is helping him out. this guy doesnt deserve her at all he never came to c her and when he did hed take her rite back like an hr later. my wife and i are preapred to fite for her. especially me she is all i have left of my sister. i need to kno how to go about getting custody of her how much it will cost me and who i should get in touch with. im currently looking for an attorney in the poplar bluff mo area. if neone has ne information to help me it will be grealty appreciated. thank you