My parents are caregivers for my 89-year-old grandmother. She is combative and verbally-abusive after 4-ish. What kind of help is needed?

She's likely "sundowning," still little understood, but it's common with Alzheimer's. People feel like they need to "do something" or "be somewhere," and this causes anxiety and hard to manage behavior.

I'd check with her doctor to see there's medication that can help. Also, planning a distracting activity such as a DVD of an old movie she may have liked, or even soft music and relaxing atmosphere can help. It's definitely a challenge, but remembering this behavior is likely fueled by fear and anxiety can help caregivers cope.
Carol