Sorry to hear about your problem.DC 100c, Notice to Quit to Recover Possession of Property is the correct form.  

The Seller In Possession (C.A.R. form SIP) form is like a lease as it has a definitive termination date.

How hard will it be to get rid of the occupants once I get possession of the property?

You have an undivided interest and possession, you can rent it, only half the income can be counted toward granny's income, until they get a DPOA when they could 1. reduce her income paying management expenses or 2. sell her 1/2 interest. 

When we first took possession of our space I fell in love with a beautiful, but dilapidated 1912 Craftsman that had been unoccupied for 2 years. 

For example if ur lease expires in 3 months and they want to stay for 6 months, you can make a case of terminating the existing and doing a new 6 month lease is best for both parties.Even without a new lease, one might consider a detailed inspection of the property conditions so you know at least what's broken or damaged at the time of your taking possession.

Unlike my parents, I don't have a bomb shelter, a 6 month supply of food from Costco, all of my wealth in precious metals or my mortgage paid off for fear that the government won't be able to take possession of a property owned "free and clear" as easily as a property that is financed.

The judge has already mandated a date to return possession regardless of who the owner is.

Instead of the 3-day Quit, use the Change in Terms notice.Highlight the points:you have no written lease you have been living here under an oral agreement on a month-to-month basisEffective 1/1/2017, the terms of your tenancy will be changed as follows:Rent of $xxx will be due on the 1st of the month and considered late after 5 days,Your lease is attached for your signature and the term will be From ___ To ____If you elect to not sign the lease on or before 1/1/2017, I will file an Unlawful Detainer action against you in court to obtain possession and that will be public record against you.If you elect to move out on 1/1/2017, I will return your deposit of $xxx

Contract clauses were really a big help - principal only mortgage - that is NO INTEREST, installment down payments, money back, right of possession, many subject to offers, delayed settlement with possession - contract candy ( also known as buyer incentives) prime rate financing - money back from seller - discounting existing current and defaulted mortgages, early pay-off discounts, substitution of collateral (my favorite one)When there is NO equity - I offer --- Contract of sale (on a skinny), subject to existing financing, immediate possession, right to assign and release of liability -- This system works well when house lacks equity.