Joint custody. How does the time get divided?

Me and my wife recently seperated. We have a stepdaughter who is 7. A daughter who is 3. She is also currently bout 16 weeks pregnant. She moved out bout two weeks ago. I don't want to divorce but she does. She says you can't divorce while you r pregnant. The attorney I talked to said it depends on what judge you get. So anyways we can't agree on how to divide up our time with our daughter. I have been doing most of the caregiving for several months due to her depresion and me having more time. Unfortunatly my daughter can't stand to go with her mother. This is unfortunate becuause it breaks my heart to send her screaming for me every time her mom takes her. I am just wanting to know what is best for my daughter and still somewhat fair without hurting my wife but most importantly our daughter any worse than this has to be? Unfortuntly the only time I am getting to see my stepdaughter is when my wife doesn't have a better option ( in her viewpoint) this is heartbreaking