There is not a direct way to do this with the scheduler. You could create a rule that triggers weekly, and flip Private Boolean each time, using it to decide whether or not to run the rule.
Or you can make it run on two specific dates each month, using a cron string like this:
As a plan 'B' you could use the Google Calendar Search app, [RELEASE] Google Calendar Search, and leverage Google's calendar tools to setup whatever schedule you need. I use it currently with a biweekly event that alters some of my automations.
To increase my WHF (Wife Happiness Factor) we have a cleaner come in every 2 weeks. I don't want them to touch any of our automated blackout blinds so I created a 'cleaning day' calendar event and I have the the Google Calendar app set a virtual switch that overrides my daily blind opening position to go full 100% and get them out of the way. Usually I just keep them ~40% open.