Best Mode Formula for 2 Month Period

You could create a beast mode based on your date field by doing something like this:

CASE WHEN MOD(MONTH(`date`),2) = 0 THEN
CONCAT(
DATE_FORMAT(DATE_SUB(`date`, interval 1 month),'%b'),'-',DATE_FORMAT(`date`,'%b'))
ELSE
CONCAT(
 DATE_FORMAT(`date`,'%b'),'-',DATE_FORMAT(DATE_ADD(`date`, interval 1 month),'%b'))
END

You would want to make sure your date field has dates for all months and then you want to make sure you click the checkbox "share calculation on dataset" when creating the beast mode and your other cards on the dashboard use that same dataset. This will ensure all the cards filter properly when selecting any of these month groups.