I live in Ohio, my niece is 3 years old. My sister is a depressed alcoholic who refuses to take her prescribed medication. She has been hospitalize twice for attempted suicide. The father is not in the picture, he has no visitation rights ( although never pursued any), no job and pays no child support. My sister lives with my parents so they are the main support for my niece. What can we ( myself or my parents) do to get temporary custody?

Go to Court, prove the child is in an unhealthy/unsafe situation, ask for custody. Active or not as a parent if the father is the acknowledged parent he will have the opportunity to get custody, and you will also have to prove him unfit.

Is there a possibility your sister would sign custody over to you without a Court action?