Adult sibling is abusive to other siblings and sometimes to our parents too. What can we do?

adult sibs take turns staying with elderly parents to provide care. One sib is abusive to the other sibs. Has been for years not just now. We try to avoid him but he often stays longer or comes early and can have a tantrum at any time. He hides our things or things we've given to parents to annoy us. How to respond to latter? Sibs want to spend time with Dad who has dementia and COPD and be helpful to him and Mom. Otherwise would just leave them all alone. Parents have always made excuses for his behavior. Mom tells us time to go if she knows he may be coming. But doesn't tell him to go. She also states "well Ill talk to him about that, when he's ina good mood." So she can't deal either. We have her talk to him about his schedule or whatever. Since we cannot talk to him or ask even a simple question w/o abusive rants.