Which of them are killable? I'm Rping a character who tries to take over the role of Jarl in Riften. Maven became the new Jarl and I try to damage her as much as I can.

I don't think any of them are essential except Maven. They're not listed in the essential NPC list, so, yes, all of Maven's kids are killable.

Good, time to put an end on Riften's corruption.

Not really since Maven is still in power.

Maven, Hemming, and Maven's bodyguard are, like most potential government workers, essential. Sibbi and Ingun are not.

Well, get the SOB's in Markarth as well while you're at it! I hate those Silver Blood more than anyone! Was pissed I couldn't ruin their status in the truce negotiation.