That's important because entering and preventing the for.mer owner from being able to return is often referred to as forcible detainer. 

The following matters are excluded from the requirement hereunder: (a) judicial or non-judicial foreclosure or other action or proceeding to enforce a deed of trust, mortgage, or installment land sale contract, (b) an unlawful detainer action, (c) the filing or enforcement of a mechanic's lien, and (d) any matter which is within the jurisdiction of a probate courtThanks!

But it sounds like the attorney is less worried about what is obviously a squatter and more worried about the lease with the detained tenant.

THE CA ASSEMBLY WILL VOTE BY MAY 31, 2018 Assembly Bill 2343 (Chiu) rewards tenants who fail to pay their rent or who remain in wrongful possession of a rental unit by delaying the unlawful detainer (UD) process by a minimum of three weeks.

Experience has taught me it can be costly when roommates squabble - - Unlawful Detainer + damages > $8kNever again!

The police will likely tell you it is a civil matter and that the owner of the property will have to file an unlawful detainer action in court.  

Until which time it's determined if any of the interlopers (squatters) have any ownership interest, you won't be able to know what form of legal possession tactics to take, whether unlawful detainer eviction, partition and QTA, forceable detainer or ejectment.

Therefore, if you just allow dogs to be in your rental so long as they are kept detained, you would probably have the same protection if not more than if you became a "dog sitter". 

(it may not legally be an eviction but some other term like "wrongful Detainer" but basically the same thing) From a practical standpoint it may not be worth the time and effort to get them to leave.

The current CA law is that unlawful detainer actions are publicly searchable unless they are resolved within 60 days of the first filing.