Can I stop ex from having visitation , for fear for there safety?

I have full custody of my two kids and my ex has suppervied visits every other week no over nites. She currently is living with boyfriend , got evicted and now lives with her mom with boyfriend. She has no job and son saw text on her phone about getting weed. Then this past weekend she filped out attacked her bother and mother broke all the picture in the house. She spent 4 days in mental health facility now claim she was druged while out drinking thats why she flipped out . I fear for my kids safety and am not letting them do visits . Legally what will happen