I often just make them stop talking about whatever it is and/or separate them, because it's so awful to listen to and sends my blood pressure through the roof, but that's not practical or productive.
Why not?
Clearly they are getting something out of the bickering, or they wouldn't do it.
I'd separate them while also making sure that neither gets what they want while separated (eg the book they're fighting over goes away for everyone). I do this regardless of fault-- I don't care who started it, if everyone's behaving rudely, everyone gets consequences.
3) DS is cute, precocious, and charming and people fuss over him. This has lessened somewhat as he's gotten older, and I think that will continue--an 8yo does not get the same attention as a 5yo. But people will say things like, "Oh, I wish I could just steal him," and "I can't stand him! He's so adorable!"
I'd also make sure that each child gets quality time with a parent, and that each one gets to spend time in situations that feel rewarding to them. It's important for everyone to feel valued.
My bet is that it may improve with time, but there's nothing wrong with keeping them separate more until then. For sanity's sake...
