I'm scared if my two oldest kids go to their dads he won't give them back seeing as we don't get…

I'm scared if my two oldest kids go to their dads he won't give them back seeing as we don't get along they haven't seen him in months but my youngest just saw his picture in a album I made for them and I can't say no he loves his dad a lot but the thought scares me we have joint custody but no set schedule that is documented by tlthe courts so if he did I couldn't do anything I'm deff filing for support Monday and custody arrangements they deserve to see both of us even if we hate eachother... feeling lost