Why aren’t you as concerned for the uncle’s hurt at having to miss his nephew’s wedding due to his religious principles? And the pain he suffered realizing the family situation he had to endure as a result of abiding by his religious principles. And why, if the other family member, is such a well known respected RY are you reluctant to PROUDLY mention who it is?
Doing what Gedolei Yisroel decree IS NORMAL. Doing otherwise is not. And Gedolei Yisroel clearly and unambigously are 100% opposed to mixed seating at a wedding.