Any idea on how I can do a waterfall projection?

@Richard LocklairOne idea is to form an agreement (partnership agreement).

Does anyone have an idea of how much a demo costs in the Los Angeles area?

I think in this way atleast within 5 to 10 years I can pay off mortgage and will end up with full property value and rentals on monthly basis (even if I don't want to earn anything till 5 years I am fine with it)- Is this a good idea to invest in commercial property like this with big downpayment?

I like the idea of starting on some items sooner than later.Ultimately, I think my "nice guy landlord" style has worked well for my one SFR rental over the past 10 years. 

I love the idea of passive income and flipping.

Ideas?

First, Rentometer is great for a ball-park figure, but it doesn't take into account a lot of information on the house (type [SF vs. duplex], square footage, condition, finishings, etc.)I would recommend reviewing rental listings on Zillow/Craigslist that are comparable to your in-laws house so you can get a better idea of what rents would be. 

Assuming you don't have an exact estimate of repair value (but likely a better idea of ARV), do you target a specific margin?

But sending proof of funds to a few wholesaler's is an interesting idea that I might try out!