Traditionally, in China, when nephews get married, uncles are the oldest. In the past, the wedding used a square table for eight people, and I had to sit in the most important position, accompanied by my uncle. When a niece marries, she usually marries her uncle in turn. My uncle is the boss and my uncle's company.
In modern weddings, because there is no need to use the square tables in the past, they are all round tables, so they don't care anymore. If possible, I can sit at the main table, accompany couples, parents, or important guests. There is no uniform rule.