Well, technically we will probably just be at a round table in the first row of tables. So we would have 8 seats. I have 5 on my side, he has 4 on his. One of his groomsman is married to one of my bridesmaids. With all the other SOs counted we would have 18. Three of those couples have kids that will be at the wedding, so we were planning on seating them at different tables. Of the other 12, it's very obvious to us what would work best for a variety of reasons (some selfish, some not, I can explain if it makes a difference). But is it a breach of etiquette to have some of them at our table and some at other tables?
We really don't think a head table with everyone is an option (if we included the kids up there, we would have 27!), we also don't want to do a sweetheart table. We could possibly do a table with just the 12 without kids, but it works better for the space if we sit at a round table.