Where to seat divorced or separated parents
Most of a table plan takes an evening. One or two rows take a week, and this is usually one of them. The good news is that there are only three real options, they are all normal, and the one you pick matters less than telling people before the day.
Ask them first
Before you draw anything, ask. A UK stationer's guide on this puts it well: ask your parents beforehand if they would be bothered about the arrangement, to avoid awkwardness on the day (Dotty About Paper). A short conversation now is easier than a seating plan that has to be redone, and sometimes the answer is that nobody minds.
The three top-table options
1. Everyone on the top table.
If your parents are still civil, they can sit at the same table, and that suits a traditional top table. That is exactly the advice Dotty About Paper gives, and it has the advantage of looking completely ordinary in the photographs. If step-parents are coming too, you may need to move the chief bridesmaid and the best man to the nearest table to make room.
2. Each parent hosting their own table.
Bridebook suggests giving each of your parents their own table, and adds that where there is real tension you might omit a top table altogether and have your parents host their own tables close to yours (Bridebook). Debrett's makes the same point: dropping the top table can help, with parents at separate tables flanked by new in-laws or members of the wedding party (Debrett's). Give each of them people they know and like, and the table becomes a treat rather than a consolation.
3. A sweetheart table for the two of you.
A caterer's guide lists a sweetheart table as a straightforward alternative, and suggests swapping a single top table for two round tables where families are blended (Dine). This is the quietest answer of the three, because nobody has to be seated next to anybody. You get ten minutes together, and both sides host.
Keep it even between the two sides
Whichever option you take, make the two sides match. Dotty About Paper's warning is the one to remember: make sure one parent is not at the more important or popular table while the other is sitting among strangers. Even distance from you, a similar number of their own friends and family on each table, and the same view of the room. If one table has to be further back, make it the one with the most company on it.
The same goes for the photographs and the speeches. If one parent is giving a speech and the other is not, think about who they are sitting with while it happens.
Step-parents and new partners
Seat couples together, and seat them with people they know. If a step-parent helped raise you, saying so with a seat is kinder than saying it in a speech. For the ceremony, the general rule is to seat both of your parents in the same row, and where that will not work, Dotty About Paper suggests putting the two couples on different sides of the room instead. Reserve those seats with cards so nobody has to work it out while the music is playing.
Tell everyone before the day
Send the plan, or at least the relevant row of it, to anyone affected while it can still be changed. A parent who learns where they are sitting from the board at the door has every right to be annoyed. A parent who was told two weeks earlier, and asked, almost never is.
It also helps to agree one small thing in advance: who walks whom in, and who sits where for the photographs. Those two questions cause more trouble on the day than the table plan ever does.
Holding two people apart on the plan
Once you know what you want, the plan should hold it for you. In Sat Pretty you say who sits together and who you'd rather keep apart, one pair at a time, and then press Auto-seat. Every guest is seated with your rules kept, and anyone on the same line of your guest list, a couple or a family, stays together automatically. If a rule cannot be kept, it says which one and what would fix it, so you find out now rather than at the venue. You can also place somebody at a table by hand, and they stay put when you seat the room again.
Then send your venue a view-only link, so the one person who really needs to know where everybody is sitting has it in writing.