What can be done about child custody and establishing paternity in my case?

My husband of 10 years and I separated 5 months ago. He is currently incarcerated in a jail in Kentucky. Our daughter was born before we were married and he is on her birth certificate and we got married while was pregnant for the boy he is also on his birth certificate. At separation I admitted to him that I don't think our son is actually his. No one seems to want to do anything about helping me establish new paternity so he isn't responsible for him as in paying child support. What can I do especially because I am fearful of what his actions are going to be when he gets out when he has already began to make threats towards me and my new boyfriend who had absolutely nothing to do with the separation. I haven't even started the divorce due to the threats he has previously made to me about if I do file. Please give me some advice.