The history of the Kelsey Brothers, and the various names of Kelseyville are summarized in Kevin Engle's two papers:

• An Act of Survival - By Kevin Engle


• Various Names Given to Kelseyville - By Kevin Engle

• The Kelsey Brothers: A California Disaster - By Dr John Parker
  This talk was an abbreviated version. Dr Parker gave a longer talk on the Kelsey Brothers at the Ely Stage Stop Museum, on Saturday October 9th, 2021. This was videotaped by Euston Productions, and can be viewed here : https://youtu.be/A6ylHq8H600


• What's In a Name: a talk by Clovice Lewis

There are two recent (March, April 2022) press articles on the proposed renaming of Kelsyville:

• Lake County group working to change the name of Kelseyville to redress violence against tribes (Press Democrat)
  (It's behind a paywall ... and appeared in print with a different title "Kelseyille reckoning with tainted legacy")
• It’s way past time Kelseyville rebranded (Lake County Record Bee)

KPFZ 88.1 FM radio has had numerous shows covering the proposed renaming. For example:

• Voice of White Plume (weekly show) hosted by Clayton Duncan
• Tribal Voices hosted by Jima and Gail Brown.
• Wordweavers. Interview with ... Audio of Dr Parker's talk at the Ely stage stop.

They were some of California's most brutal slave owners: Their deaths sparked a massacre - San Francisco Chronicle.

The ACLU (Northern California) has a series on "Gold Chains - The hidden history of slavery in California". Of particular interest are:

Bloody Island Massacre As many as 200 Pomo were killed on the island and in the surrounding area. Many women and children were stabbed with bayonets. One of the few survivors was a 6-year-old girl named Ni’ka, later known as Lucy Moore, who hid in the bloodied waters and survived by breathing air through a reed. The seeds of this bloody conflict can be traced back to 1847 when two white settlers, Charles Stone and Andrew Kelsey, bought a cattle ranch where they kept several hundred local Pomo men as slave laborers. 

Rosa: Kidnapped, Sold, and Killed Rosa was between 10 and 12 years old and was believed to be from either the Yuki or Pomo tribe. In the winter of 1862, she was beaten and left to die in a snowstorm by a woman who had been granted legal custody of her under the law. 

A History of Napa and Lake Counties - By Lyman L. Palmer 1881 This is a full-text version.
A History of Napa and Lake Counties - By Lyman L. Palmer 1881
This google verison is searchable, but not all pages are available.

This book is rather old, but does represent a contemporary view.