Threat to life

I have a case with my ex-wife in family court from past 6years and we are having a daughter which is under her custody. now at this stage while recording my witnesses and evidence, I have been receiving threats to my life and my minor daughter from my ex- brother in-laws without provocation. I have been ignoring them from long time but I came to know that my ex-in-laws has committed crime in past (kidnapping) for which they went through proper trail (365) and solved through compensation to opponent party and next they are having fake police application on some other persons as well just to take revenge, which later on they drawn/ get back. as my ex-in-laws is of destructive mentality and uneducated. So i am not calling for trouble. But now they have started sending threats on face and following me by unknown peoples to make me more fear. in past I have verbally reported in family court but they didn't took it seriously. How can I pursue further to ensure that the trouble makers are brought to law and to protect my self and family P.S. I have complete legal record of my ex-in-laws where they have committed crimes or fake legal actions in past please help me out i am very depressed... thanking in advance