A few years back a Mizrachi cousin of mine made a chasana. There was mixed seating though no mixed dancing. My cousin of course invited her uncles. One is a very choshiv Litfish Rosh Yeshiva whom everybody has heard of. The other was Chasidish. The Chasidish uncle refused to come while the Litfish R”Y uncle came and sat at the table with my family members (who are not related to him).
He sat there with his wife and married children and he spoke very normally to my mother and my siblings – both men and women. He is a very very frum man and heads one of the most stellar Yeshivos of our time. It was all very normal and pleasant.
If you look at pictures of chassanas from 50 years ago – there was mixed seating there as well. I am not advocating mixed seating – but it is not the biggest Aveira as we can see that our Gedolim participated many events that had it.
We are family friends of an alter Yid from Litta who is in his 90s and related to many Gedolim of yesteryears (Reb Moishe, Reb Yaakov etc.) I have seen pictures of his chassanaha – and all the R”Y are sitting there – with their wives – at the same table.
Of course – they are not teenagers – LOL.