I agree that it is not a good idea to brush it off, "attention seeking behavior" is simply a way children (and adults) express that they are in pain or have needs that they are having difficulty getting met.
Ditto
One of my children has said this when they are upset ("I want to kill myself") - although it's not a "real" thought - as in, she's not literally wanting to kill herself when she says it - it is an expression of a very real emotion that she's struggling with. My dd struggles with self-esteem, even though you'd never see it looking in from the outside.She's built up a protective wall to keep away those thoughts of self-doubt and approaches life with a lot of bravado. The thoughts of (and the verbalization of) "I want to kill myself" usually happens after a fight or when her emotional defenses have been threatened. Please know I'm not suggesting this is what's up with your ds, just illustrating what is happening with one kid when she says "I want to kill myself".
This may not apply, but fwiw, not all siblings "fight all the time". I have three kids, and also have a lot of nieces and nephews and friends with kids. Some siblings fight, some don't, rarely have I seen siblings who fight all the time. My two dds have polar opposite personalities and one is a bit of an antagonizer and they fight - way more than I want them to - but even with their contentious relationship they also have times that they play together and get along for periods of time. I have no idea if your children are literally fighting all the time or if that's just an expression and they're fighting now and then... but if they are fighting all the time, I'd try to think through what's at the root of the constant fighting.
Best wishes,
polarbear
