I have the same problem with bi-weekly reminders for payroll, and stumbled across the biweekly repeat. Try this.
1. Go to the online Google Calendar.
2. Create the event.
3. It may not work when you first create the event, but it worked after I created an even with a monthly repeat reminder. When I went back to edit the event by clicking on it in my online google calendar, scroll down to the reminder, click "edit" on the repeat reminder.
4. Choose Weekly from the drop down list on "Repeats:" and then select "2" from the drop down list on "Repeat Every __ Weeks"
5. Click Done to save it.
Hope this helps!