What can you do when the higher ups are the bullies? Like, even higher than the manager?

Just do your possible best, especially for the patients; because God is the overall boss who sees everything.

Not really much you can do, it's like that a lot of places. The best advice though is start a paper trail. Document to have proof of bullying, hostile work environment, and/or harassment.
Anytime you have a conversation with a manager or higher up if it's important follow up with an email summarizing the conversation. And send it to the person you talked to. And beyond that, Show up, be on time, do your job and go home. Don't give them ammunition. Don't make waves. It's not fair, I know, but unfortunately they usually have the upper hand and they know it, that's why they do it.

There are 2 things you can do. HR may help, but they have the same bosses sometimes. Also, since it's the manager, go to the CNO before HR to follow Chain of Command & then HR. If all of your team is in agreement, you can go as a group. If you are the only one being treated poorly it may be best to change units, but if the manager always has 1 person picked out and for misery you will want to go to let HR know why you changed units.