You can link guests so they share a bidder number.  The easiest method is to create a couples ticket type that automatically shares a bidder number.  You can also link guests manually prior to your event or from the check-in screen at your event.  You can Unlink guests on this same page.

To link at the time of ticket sales, create a Couples ticket and check the box "Share one bidder number for all guests on this ticket (Auto Linking)?."  

Preview how to link guests at check-in.

Note:  guests cannot be linked/unlinked once they have checked in.   If you are certain they have not placed any bids using their bidder number, you can undo check-in on the Ticket Page:  find the ticket > click on Edit Guest > uncheck "Checked In" box and Save.