Since no canon was specified, I will assume Hobbit. 🙂
1. Dori and Balin have basically the same superpower – they know things. This doesn’t mean they can’t be surprised or miss things (especially if you’re Nori). Dwalin, on the other hand, doesn’t bother most of the time. Balin is his big brother and always knew everything anyway.
2. The Durin clan, being from an old blood, wealthy family, generally use their powers to the benefit of the government/system. It’s always meant the best for them, so they don’t even think of possibilities. Dori’s gang is far more vigilante. They help victims, including victims of the system, so they often go against the police and the government.
3. Dwalin and Nori actually met at an ice cream parlor. Dwalin was indulging his sweet tooth. Nori was actually getting something for Ori, but when he saw Dwalin he decided that could wait.
4. Dwalin is probably the most gentle and safe of his family, but none of them – himself included – see it that way. Because of his berserker rage, he has developed 100% control of himself. It is ironclad and can withstand extreme provocation (he can beat people up while calm if needed). They all see the flaming rage and not the control. It is sad.
5. Dori’s “villain origin” – depending on if you want to consider him a villain – is pretty much that he just got tired of things like police entering a house firing and killing children and non violent offenders if they were black/poor but calmly talking down armed and dangerous white men.