Not yet. I think right now it makes sense. In 3 months it will probably be less necessary. September is far off. Maybe he should wait a few months to decide.
Where I live there are groups that are back to normal because everyone is vaccinated in the room. Examples: Card games (10 tables in a room sometimes). Practice for performing dance groups. The list goes on. I don’t know if they said vaccinated people only, or if all the people returning simply are vaccinated. Also, dinner with friends, friends who know each other are vaccinated are now willing to go out together and sit at the same table.
Maybe he can ask people not vaccinated to wear a mask or to get tested or quarantine. Can his dad be trusted to quarantine before the wedding? A lot of anti-vaxxers never took covid seriously and when they say they are being careful their idea of quarantine and careful is not really quarantining.