Every wedding has its difficult dynamics. The divorced parents who have not spoken in a decade. The feuding relatives who are both invited and cannot both be seated in the same room without a mediator. The step-parent who arrived after the invitations were planned and before they were sent. The sibling who was not asked to be in the wedding party and has not recovered. These are not problems to be solved. They are circumstances to be managed, and the management begins with the understanding that you cannot make everyone happy. You can only make the day coherent.
The divorced parents are the most common and the most consequential. The first principle is that the wedding is the couple's day, not the parents', and the couple's comfort is the priority. If the divorced parents cannot be in the same room, they cannot both be at the wedding, and the couple must decide — early, and with kindness — how to proceed. If they can be in the same room but not together, the management is in the seating and the processional. Each parent is seated at their own table, with their own family and partner. Each parent walks down the aisle separately, or is escorted by the partner who is present. The couple may walk down the aisle together, or with one parent, or with neither. There is no correct answer. There is only the answer that causes the least harm, and the couple is the one who decides it.
The step-parent. If a parent has a new partner, that partner is included in the wedding to the extent that the couple wishes and the relationship allows. The step-parent is seated with the parent. The step-parent is not in the receiving line unless the couple specifically and genuinely wishes it. The step-parent is not in the processional unless the couple specifically and genuinely wishes it. The biological parent retains precedence in all formal roles. This is not a judgement of the step-parent. It is a recognition of the structure of the family, and it prevents the kind of ambiguity that produces hurt feelings on all sides.
The feuding relatives. If two guests are known to quarrel, separate them. Not by one seat. By a table, at minimum, and by a clear line of sight if possible. Do not seat them where they will encounter each other at the bar, at the buffet, or at the entrance. If the feud is serious enough that their presence together is a genuine risk, speak to each privately before the wedding and ask for their cooperation in keeping the peace for the day. Most people, asked directly, will agree. The ones who will not are telling you something, and you may need to reconsider the invitation.
The sibling who was not included in the wedding party. This is the wound that is most easily avoided and most often inflicted. If you have chosen a wedding party that does not include a sibling, tell the sibling before the announcement, and tell them why. The reason does not need to be elaborate. It needs to be honest. A sibling who learns of their exclusion from the wedding party through the engagement photos, or through the family, is a sibling who has been given a wound that the wedding itself will not heal. Give them a role instead — a reading, a processional escort, a toast — and the exclusion becomes an inclusion of a different kind.
The principle beneath all of this is simple. You cannot control the feelings of the people at your wedding. You can control the structure you give them. A clear structure — who sits where, who walks when, who speaks, who is included and how — removes the ambiguity that breeds resentment. The people who love you will accept the structure if it is fair and if it is explained. The people who do not accept it were going to be unhappy regardless, and you are not responsible for that. Be kind, be clear, and let the day be yours.