I hope that this is just an empty threat. If she's on meth I hope the last thing she'll want to have around the children. My guess is that unless the kids are injured, hungry, or she is high.....cps can't do anything. I know we have had to call cps and kids are not removed from the home where it clearly seems they should be. If she comes and takes them, call then, tell her you are calling them right away. The husband on probation will not want cps near them.
This is a completely uneducated guess however. Find out all you can about what the state allows, how and if you can intervene, and the protocol for everything. Inform yourself, make calls and write everything down, especially the persons name you speak to. I'm so sorry, it's hard enough taking care of small children all day, that pales in comparison to the worry difficult child is causing you right now. hugs.