I don't think you need to read the main series to understand it although this does tie into the Futures End Booster Gold one shot. You probably can skip the FEBG issue as only the end really matters. Most of Covenvegance is about cities from different timelines fighting. This two parter is mainly about the Carter family and figuring out what to do. The city aspect does come into play since they kind of have to move but their more behind the scenes.