Try splitting the coverages with two different carriers.

At the same time no matter how much excess insurance coverage you obtain, there will always be a policy exception for gross negligence and even negligence will likely be covered only under reservations of rights meaning the carrier can opt not to provide coverage. 

If rates keep going up, and we then have 2-3 years of no hurricanes, the insurance carriers will be very profitable, and will start to chase business, lowering premiums. 

Not many carriers offer this but the one we use that has it extends that coverage to a 3rd party (property manager) as they are probably the one who did the thing getting you (property owner) sued for the fair housing or wrongful eviction.

When doing renovations to a property you should notify the carrier in advance and they may require a builders risk policy as well.

And don’t pay anyone or sign anything before you get your carrier involved.

However, due to it being:1) In the state of California2) A shared home, rather than an outright external property being rented...the default insurance company on offer advised that many carriers are pulling out of CA and that I should go to a local insurance agency.My current insurance for home policy does not offer a "home-sharing endorsement" but only a separate renter's insurance, which would complicate things, since it's for traveling professionals, and they're not going to be booking for 12 straight months.

They seem like a newer company so I am trying to see if they are worth jumping ship from my existing carrier for.Thanks

Is the Tapco policy with an admitted carrier?

Check with your insurance carrier.