You can create a group membership level and then create groups for each family. You can also add a database field which you can set to the same unique value for each couple. For mailing purposes you can then search for this unique code and send an email blast.
Another alternative is to use the same email (sort of) for each couple, e.g. if husband's email is hus@hus.com, then set wife's email to hus+wife@hus.com. Normally both of these emails would go to the same email box and a keyword search for 'hus' would return both records.
Jim Sympathy, Fluid Apricot