You may at least want to take a look at vdirsyncer[0]. Assuming all of your sources run CalDAV that you can hit than you can at least extract the events. I use it for backup for a calendar of my own (so I don't know what I would use to "merge" multiple synced calendars into a singular view but maybe you could do that via a "master" account an write all the other events to it?)
[0]http://vdirsyncer.pimutils.org/en/stable/