I cannot stop worrying about my parent's in assisted living. Any advice?

I'm not clear if the issue is that something might have happened or that you think you are worrying yourself too much.

If it's that you're worrying yourself too much, there's not a lot anyone else can do. You have to find a way to be at peace with some of what's going on, there. If you have what you think are real concerns, maybe you can speak with the facility about your worries to see if they have more information for you.

Is this a sudden change in dad's mental status? Get him to his doc to check for a uti or other infection. Fax a note to the doctor beforehand about dad's recent behavior change.
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It may be best to separate them in assisted living. It sounds like Dad may have some dementia issues or something else going on. It would not be the first time.

Does Mom have any health or dementia issues?

Could you tell us some more about your parent' health? Does your dad have dementia or Alzheimer's? If so, what meds is he taking? Has your dad just recently started being confrontational? Is your mother afraid that he might get violent with her or with someone at the assisting living place?