I don’t think it’s as uncommon as it might appear in real life but people generally don’t talk about such things.
I’m nc with my sister she’s a bloody nightmare. Been nc with her twice before and was talked around but I won’t be this time. It’s been 6/7 years? There are certain good aspects of her I miss nobody is all bad but the bad far outweighed the good and caused considerable stress and arguments with others.
My mum is 1 of 6 but 1 of the others is also a nightmare. They are included in major family events but otherwise aren’t really part of things largely as they’re unbelievably awkward and snobby about certain activities the others do together.
My dad is 1 of 5 and they are constantly falling out with each other! There are 2 that are always “friends” but yes constant arguments some going back decades! Parents take very little to do with them now. Polite communication mostly.
Various friends I know privately that they have fallen out with or are no contact with or vlc with siblings but it’s not public knowledge. Although 1 situation did spectacularly blow up on fb recently but I happen to know the family very well and quite honestly it was a LONG time coming and the person who blew up was very much the scapegoat and I was actually really pleased to see them finally stand up for themselves. Some home truths were posted and when asked I’ll admit I didn’t tell them otherwise and they fell out with me then! Not a problem they were in the wrong and I wasn’t going to say otherwise just to salve their conscience.
Thinking about it I know very few people who get along well with all siblings. I think that’s more rare actually. Going off my fb friends (all people I know well) I’d say less than a dozen genuinely have good relationships with siblings out of over 200 people.
The rest either simply aren’t close (usually due to big age gaps) or are actively anti each other.
I’m not including “normal” sibling rivalry/bickering but truly not having much in common, having very different opinions on key issues, having had massive fall outs due to dreadful behaviour on the part of one of them.