Here are some examples of 'good squatters'....who turn 'unused space' into community garden 'improvements'...but got zapped by the system:
(your problem occupants do not qualify as such)
https://www.dailymail.co.uk/news/article-3147053/Keen-gardener-spent-5-000-turning-derelict-land-block-flats-urban-oasis-ordered-rip-didn-t-permission.html
https://www.nytimes.com/2018/10/26/us/white-women-calling-police-black-men.html
https://www.pe.com/2013/08/16/san-jacinto-community-garden-removal-ordered/
Being in California, I wouldn't mess with the utilities or harass them without due (legal) notice.
Do this carefully.
I don't think your particular attorney is correct, unless you are willing to risk additional compounding legal fees, depending on the occupants.
Reconsider other attorneys. It is an emotional time.
(they might be very experienced with the system and are 'disadvantaged' in some way...new kids included)
It is California.
Unless you are
guaranteed a local judge sympathetic to owners, don't mess with the utilities!
In the end...it is a mostly free house probably to the next of kin, and a time to wrap up that part of your life.
Fixing up to sell will be your next challenge.
Take the higher route.