It is up to her to let your siblings know the rules and enforce them. 

Not to mention other pieces of legislation that make being a landlord in CA not the most ideal. 

To my understanding the law states here that you either have to have an ownership interest in the property or you have to have a RE brokers license to collect and enforce a lease.Collecting rent and enforcing a least for Properties in an LLC:1.

If we don't tell them we're the owner, they might start getting suspicious when they see us making these changes.The last thing we would want is for them to feel like we're being dishonest landlords, but we also want to maintain some boundaries and make it a little easier to enforce rules if need be.Thanks for your help!

Airbnb won't support a fee to the guest staying longer unless you have it in your listing or rules but if you do, and it was an inconvenience for you or your cleaning team, I would enforce the rules you've created.

This MFH property is 50+ years old and the City wants to enforce recent building codes on this property.

I've been sorting out 24-1098 with existing leases at my job, where it's created some difficult knots to untangle with the timing of affordable housing tenant recertifications and the offer/notice timelines.But that aside, the law just imposes more formality on lease enforcement, whether or not it comes to a forcible eviction.

@Yaakov S.I would definitely start enforcing the late fee and see if anything changes.

"It is not legal to divide an existing dwelling unit into separated living spaces, thereby creating new dwelling units, without first obtaining DOB work permits,"  That would be an illegal conversion and can result in violations and other enforcement actions.

The paper you sign will not be enforceable since you aren't holding a deposit.