Culturally/legally I'd never claim to understand what is "acceptable" in Japan, but I really wish that Yuzuru and his family would sue the living daylights out of these people that are endangering their safety.
For a couple to split up due to external pressure is a terrible, awful thing. A relationship, especially a romantic kind, is intimate and private. It might have been a mutual decision to get a divorce, but there were "participants" involved in this outcome who shouldn't have had any presence in their relationship at all.
I just want Yuzuru to go total scorched-earth on these people who are hellbent on destroying his life. They aren't going to learn or feel remorse, especially since from their perspective, they got exactly what they wanted. It's not fair that the world always demands a kind individual to "be the bigger person" and let others step all over them. And sorry if I'd like to remain naive and believe that we should be allowed to make this world fair, and that taking measures to protect your own happiness and safety isn't wrong. Especially when it comes to someone who has only brought joy to others.
Best wishes to him and his family. I hope they heal from this heartbreak.