The parents of the bride always sit in the first pew or row on the left, facing where the ceremony will be held; the groom’s parents sit in the first row on the right. At same-sex marriage ceremonies, the couple might assign each family a side, and seat guests on "Bill's side" or "Kevin's side" accordingly. If the site has two aisles, the congregation sits in the center section. The bride’s parents sit on the left side of the center section and the groom’s parents on the right.
Widowed parents of either the bride or groom may prefer to have someone by their side during the ceremony, and it is perfectly correct to do so. Their companion is treated as an honored guest.
When either the bride or groom’s parents are divorced the seating needs to be planned carefully and the ushers need clear instructions. It can be tricky: Divorced parents may or may not get along, or the bride may be close to one parent and not the other. Tact and diplomacy will be critical for keeping the peace.
In the lucky event that all the parties get along, there’s no reason why the divorced parents cannot share the front row. But when there is strain or outright bitterness, it’s necessary to use a careful, well-thought-out alternative plan that keeps the parties separated.
When divorced parents sit separately, and using the bride’s parents as an example, her mother (and stepfather, if Mom has remarried) sits in the front row. Members of her mother’s immediate family—the bride’s grandparents, any siblings who aren’t attendants, and aunts, uncles, and their spouses—sit immediately behind in the next one or two rows. The bride’s father, after escorting his daughter up the aisle and presenting her to the groom, sits in the next row behind the bride’s mother’s family—usually the third or fourth—with his wife and their family members. This protocol is followed even if the bride’s father is hosting the wedding.
When the groom’s parents are divorced, they’re seated in the same manner.
Behind the front rows, several rows on either side of the center aisle are reserved for the immediate families of the couple. These guests may have been sent pew cards to show their usher, or the usher may keep a list of guests to be seated in the first few rows.
It is fine not to have "sides" for wedding seating, instead inviting guests to sit where they like. This is sometimes done when one half of the couple has significantly more guests than the other, or at a more informal wedding. Regardless the reason, the front seats are still usually reserved for the couple's close family, to be sure they will have a good view.