Not attending a mixed gathering wedding

Q: Is my view point good or extremists? I never ask about what the bride to be will wear on her wedding day as here she wears fancy clothes infront of na mharam people, which I totally disagree with. I haven't asked my own sister due to same reasons and she says that I am an extremists. I am also not attending her wedding as there will be mix gathering and music, am I right on my stance?

Hitting someone for stealing

Q: I'm trying to find clarity on a situation where a brother got caught with something that was not his and in the end admitted to stealing it. The stolen item was returned and the brother refused to accept the punishment. So after he refused to accept the punishment, some brothers lured him into a room, beat him and robbed him of all his property, saying that it was sunah.

Insha Allah you can assist to either support their actions or to show them where they went wrong.