Shalom and Haredim

Hello Rabbi
Yesterday I was at my Haredi friend’s wort. When I asked if it was customary to say Mazal Tov to the bride, he said that of course not. As we talked further, he also explained to me that even after the wedding, she is not allowed to talk to his brothers. To my surprise, after doing some research, I saw that there seems to be broad agreement on this in the Gemara and Poskim, at least regarding talk that can lead to affection.
My wife and I, as national religious people, regularly invite and are invited to Shabbat meals with other young couples, and yes, I also get to talk to the woman at the event, even things of friendship and affection (needless to say, everything is respectful and within the bounds of modesty, at least that’s what I thought until now), and at family events there is no point in talking at all about the teasing of aunts, cousins, sisters-in-law, etc.
I’m trying to understand whether there really is a problem with this, and if so, how it seems that the majority of the national public, or at least mine, which claims to observe all of the halacha and adhere to both the mild and the severe, simply lives as if it doesn’t exist, and if there is an answer, what is the basis of the disagreement between us and the Haredim on this matter.
It also brings to my attention other random laws that seem indisputable and yet no one seems to really live by them, such as listening to music while there is no Temple and a few other things that I am probably missing (I didn’t really look into the issue of music, I just looked in the Shulchan Aruch).
thanks