Here’s a 1963 home movie -- clip 2 of 4 -- of two sisters getting married at the same time in Michigan. To clarify, the sisters are marrying two different men and not each other. 

Shot of groomsmen. Bridesmaids and flower girls walk down the aisle. The two brides walk up the aisle with their father in the middle. Brides and grooms are at the altar. Priest addresses the couple. One couple exchanges vows. Couple kneels down at altar. Priest addresses other couple as they are kneeling. Bride and groom walk down the aisle. Second bride and groom walk down the aisle.