Hohenbergs requires you to get the Habsburgs in power (Austria or Hungary) first. Once you've done that, you will eventually get an event where you can either peacefully give power to the Hohenbergs for -100 political power or have a civil war and pick a side. I think you might have to give extra power to the burgeoisie at some point through an event to have this happen. Although, I usually do that anyway so I don't know if it is actually required.

Einstein comes to power through building a technocracy in Israel. I don't know if he can come to power in any other nations like Leon Trotsky can.

Edit: There is also an event to block the democratic branch. I'm pretty sure you need to allow Democracy (essentially every event response should empower either the democratic power or lessen authoritarian power).