If the ADU actually costs you $500K, it's barely worth it in terms of cashflow.

That part was actually straightforward to get done.   

I would have actually keep the property and corporate leased or air bnb each unit.

These dates can be provided by the contractor, but should be something agreed to upfront.

If you provide a scope of what you are demo-ing, you may have better luck with someone's experience to comment here, but costs can vary regionally, so a local contractor would give you the best actual estimate. 

Report it to the credit reporting companies ASAP.Talk to an attorney ASAP.Document every call, email, and message you leave with time and date. 

Once the title is clear of those pesky old liens, you'll be good to go.This is not legal advice, so speak with your attorney for actual procedural issues.Keep investing and moving forward!

The neighbor is now giving my tenant a hard time by saying that his property actually extends into the driveway of the property that I own. 

We have about a dozen properties we're looking at for this retrospective and all the results are various due to different purchase dates, timing and etc.

Honestly, I would have never guessed that this market is actually not great for rental investments, but it is really strong for fixes and flips.