In short, I'm looking for a solution on Ubuntu/Linux that will allow me to keep two calendars, each managed by a remote CalDAV server with a web interface, in sync, in the sense that any change I make on one of calendars through its web interface would be propagated, with minimal delay, to the other. Each of the web interfaces allows me to subscribe to remote calendars, but the subscriptions are unfortunately read-only, so that doesn't help.
I've looked at a few approaches already, but haven't found anything satisfactory. The most promising seemed to be syncevolution, which could be used to synchronize the remote calendars with local databases, but it wasn't clear whether I could (1) sync them both to a single local database or (2) sync them to separate local databases but keep these local databases in sync somehow. One of these would be required to do what I want.
Is there a way to achieve my aim here?