You may wish to offer a discount for buying multiple memberships at once - for example, to encourage dual membership sales - which you can do by creating quantity price breaks.
Enable quantity price breaks
Create a membership bucket
From the membership bucket's General settings page, scroll down to Quantity price breaks and select the checkbox
Specify the minimum quantity necessary to trigger the price break, and what the price per membership will be when the minimum number is purchased
Click Add Another Price Break to add additional quantities and prices
Once you've added all the price breaks you want, click Save
Want to sell this membership on your site? Read our article about selling memberships!