I have a 2 1/2 year old son with my wife. I also have a step daughter who is 10 years old. I am in the process of leaving my wife and I am want custody of my son. I would also want custody of my stepdaughter, however her father is active in her life. Besides the fact that I want custody of my son for my own reasons of wanting to be with him everyday, I am worried about leaving him with his mother. My wife suffers from bi-polar disorder and over the last year she has stopped taking her medication. During this time, she has become verbally abusive towards my son. I have been the primary parent in my son's life *examples - wake up with him and give him breakfast, give him his bath's, give him dinner, take him to daycare, put him to bed and read him bed time story.
There are too many instances to list of where I have come home from work to find my son alone in dangerous situations while my wife is asleep. Any helpful advice, tips etc would be greatly appreciated. I live in Central NJ.
Thank you.

Yes, hire an attorney! Your attorney can help you prepare a case against your wife that she is an unfit parent.

In the meantime you need to create a journal that lists every incident of neglect or abuse against both children.

You can try for custody of your step daughter, but if the father objects and wants custody himself, he will probably get it. But there is no reason you can't have custody and he continues with the same level of activity that he now has.