Question about parental rights and marriage

My husband and I are separated; I live in California and he now lives in Texas. He has not seen our children in years, and shows no interest in ever doing so again; he's also already signed his rights over to his other daughter. We are not legally divorced yet, as he refuses to file and I cannot afford to since he never pays his child support and I have our children to support. My question is: is there any way that I could have him sign over his parental rights even though we are still legally married? I do want the divorce and plan to file, but unfortunately, it is not financially possible right now. I would let the issue sit until the divorce and take care of it then, but I do not trust their father. And if it is at all possible to have him sign his rights away, how would I go about this since we live in separate states? I can't really afford a lawyer but I will go to one if need be.