What where your first doubts?

If the tenant been squating there for 3 months unpaid rent, there is no doubt that tenants will squat till however long it takes to get the tenant out with eviction.

I doubt I am much help but feel free to pm me if you think I can answer anymore questions.

Legally, I doubt anyone would bat an eye over a landlord changing out a shower trim kit.

Without personal experience in the field, I doubt you will get very far.You’ll have to do a lot of marketing to real estate brokerages, REI meetups, etc. to generate clients.Also, @Steve Morris Yes, here the state does set the title insurance rates, but they set the Maximum rate.  

I doubt the event is even for real. 

. - Hey David, I doubt you’ll find many agents who specialize in duplexes because it’s such a small niche in most markets.

Through his father passing his tax advisor told him that he is going to make too much money this year that he might have to sell the house at a loss.I rarely say a professional should be fired after getting a mere bird's eye view of the situation...I like to give the benefit of the doubt, but any tax advisor who advises the above should be fired on the spot. 

Personally I doubt your property will cash flow and would be very reluctant to get involved in CA housing/politics.

What you have there is like what Nathan said, plywood subfloor on a cement slab with VCT on top of it.