Blended Family Ceremony Seating
For step-relatives, be sure your Planner or Ushers know who they are. Step-relatives should be escorted to their seats before genetic/birth relatives. For instance, step-grandparents would be ushered to the 3rd row before birth grandparents are ushered to the 2nd row. To avoid confusion, reserve a few extra rows directly behind immediate family for step-grandparents and stepsiblings.
When parents are divorced, in either the Brides or Grooms family, seat the parent who primarily raised the Bride or Groom in the front row with his/her spouse, and seat the other parent and his/her spouse in the 2nd or 3rd row. If relations are amicable, birth parents may sit beside each other in the first row, or they may share the front row with stepparents. Discuss this in advance to avoid awkward moments, and have your Planner or Officiant put actual names on the chairs/pews, to avoid confusion as the ceremony approaches.
The bride's mother is always seated last at a Christian & often in general, non-faith based North American ceremonies; the groom's mother is seated just before her. (In Jewish ceremonies, parents stand under the huppah with the couple). The seating of the bride's mother signals that the ceremony is about to begin.
Blended Family Reception Seating
Traditionally, parents & grandparents from both families are seated together, but if the Brides or Grooms parents are divorced, and seating them together will create any tension, each set of parents can host their own table of close family and/or friends. This could mean up to four parents' tables, depending on your situation.
Remember, when dealing with blended families, be flexible. Set it up in whatever way best reduces your stress as a couple. If you're unsure, always strike up a conversation with the parents in question, to help you make your final decision.
