his opinion on each sibling?
he doesn’t really remember henrik that much, he just knows what his family has told him. he was only a kid when he died, he mourned him then but hasn’t really mourned him since. he doesn’t know how to mourn someone he doesn’t even really know or remember. he thinks of him as the boy who died and ruined his life, he doesn’t really say that because he knows it’s touchy for his family and it’s a line he’s not going to cross but henrik dying is why kol lost his magic. henrik dying is why kol became a monster ( it’s esther’s fault not his but, it’s still true. ).
his opinion on klaus is … complicated. he trusts him when it’s convenient for him, and deep down he does love klaus but klaus has also fucked him over many times. klaus has daggered him too many times for kol to ever fully trust him, but kol has allied with him / sided with him before and would again. but he’ll never really forgive him for the daggering, or for in kol’s eyes, hating him.
he’ll always be scared of him, too. for as long as klaus has daggers, kol will be scared of him deep down ( maybe even when he doesn’t, his fear of him is now kind of instinctually rooted due to centuries of the same shit. ). sometimes he thinks he loves klaus, thinks he could trust him, thinks maybe he’s what a brother is supposed to be but it never lasts long. klaus at times has been kol’s favourite sibling just because he went along with kol’s killing antics, when they were being mischievous/causing trouble together, he actually felt like his brother. almost believed in always and forever.
he doesn’t hate him. to put it plainly, he doesn’t hate elijah. something he’s envious of him, or scared of him, but he doesn’t hate him. he’s been angry at him a lot, especially after what happened with davina, and especially since elijah has been at klaus’ side helping him dagger kol every single shown time it happened. kol thinks he’s overly righteous, or at least thinks / acts like he’s someone who’s more righteous and virtuous than the rest of them. kol wishes elijah looked out for him like he did for klaus, wishes he protected him like he did klaus. but it’s very doubtful he’d ever admit that.
kol hates him. thinks he’s a big ol’ dick. mourned him, yes. cried for him, yes. but he killed kol, he cursed him to die in front of the girl he loved, the only girl he’d ever loved. that’s unforgivable, plus he knew it was kol’s biggest fear, and he did it anyway. he was supposed to be his brother, family isn’t supposed to let each other die let alone kill them. they’ve never gotten along due to opposite personalities, but in finn’s death kol was still sad to the point of crying while tossing his ashes.
kol thinks he’s just a giant asshole who thinks he’s better than kol just because he doesn’t kill people the same way but they’re all the same thing, they all suffered. kol thinks he acts like he’s higher than him and kol thinks he’s a pretentious douche and has never really liked him, not since they were tiny kids.
he’s considered them partners in crime at more point that one ( they’ve caused mischief together for a long time, most of their lives actually. ). as the youngest living mikaelson siblings they were close but she still crossed him, which is why he crossed her back ( he’s forgiven her for that seeing as he got his revenge but you know. ).. she’s also been classified as his favourite sibling many times throughout their lives but they still bicker, because well, they’re mikaelsons. he helps her whenever she needs him, he doesn’t approve of some of the ... romantic choices she’s made in the past but he’s also not exactly the best partner ( he never claimed to not be hypocritical. ). out of the siblings she seems to know him better than any of them, and he knows that.
before what happened with davina, kol might’ve had a higher opinion of her but he’ll never forgive her for what she did. never. he’s quoted to say ‘i never for a second wanted you’ which kind of says it all. he despises her for choosing finn over him, for not letting him attack and acting like it’s possible to mend the wound of finn literally murdering him. he’s civil to her sometimes, and was civil to her before he knew who she was but he really just don’t like her. she’s never proved herself to be someone he should love, or trust. he might have a slight soft spot for her because she’s a mikaelson witch, and maybe he also envies her for that ( he does. ). she has the magic he wishes he had.