My parents bought 2 condo/townhomes a few years ago.

Ideally I'd like for my retired parents to live in one unit and have the option to sell the second unit (as you mention, an attempt to making the living area as close to free as possible). 

I am considering buying my parents home.

And no offense intended but these parents are usually "helicopter parents" that constantly calling or email trying to argue with me about the lease agreement or why little Joey can't get the oven to work or why can't little Joey add three more roommates to help with his rent.Cosigners are way too much work and trouble.

Stay over parents, friends, uncles, aunts, brother whoever that can accommodate you for free for about a month. 

My parents, who swore for most of my life they would never live in California and my dad who is super-frugal so cringes at the thought of costs, ended up moving here and they tell people all day long they realize why it costs so much more--it's amazing.

I didn't have anything growing up and I saw how hard my parents worked.

My property management company left things out of the lease and the tenants filed for mediation and are asking for below market rent.It hurts, but I'm okay taking the hit on the remaining 6 months of the lease, but want to protect myself from being subject to California rent control if the tenants stay beyond the initial lease.I don't want to be stuck below market for any time beyond the initial lease.The tenants are college students with lawyers for parents/co-signers (adding this to my book of red flags!).

This allows your parents to co-sign for an FHA loan with you.

I will allow a "Personal Guarantor" when the tenant is a student- usually it's a parent that signs since they are going to be paying the rent directly or indirectly anyways.