Dad with dementia has become hostile, angry with staff and residents of facility. Any advice?

If this is a sudden change in mental status, report it to his MD immediately. He could have UTI, he could have some other kind of infection, he may have had a stroke.

A change in mental status in a dementia patient needs to be investigated medically.

MD consult at once. There are sometimes medications that can help. He will almost certainly have, without some controls, to be moved to a higher level of care, and unfortunately it will be a less caring level of care. I hope you will get some answers to what might help. But this is a medical need now.