custody of a child

my husabnd and i are trying to get ful custody of his two year old daughter and we have started the custody papers but they told us that we needed proof that the mother is unfit. well the mother lives in sandusky ohio and we stay in cleveland ohio how are we suppose to know what is going on? we know the mother mother drinks everyday and smoke weed also but how would we be able to prove this to the judge? my husband is also paying child support . What do we need to do to get his daughter? - Is this your question? Add additional information