Is there a way I can "co-sign" with one of my parent's credit cards and be on their credit history in order to boost my credit score? 

It's really your choice if you want to select a home that has already been leased prior to closing or not. 

Vaughn is to be selected as a director or nominee of Company.One document noted she owned 22% of rad managment. 

However, I cannot be signed into both her account and my own VRBO for my 2 properties at the same time.

How, and why, do you select them?

A sub S election will probably block the free stepped up basis benefit though.

Quote from @Tod DuBois: Another Furnished Finder POT cancelled on me after I went out of my way and paid to review them on Key Check and signed up for Key Check contracts, made two contracts, allowed a pet and still, two days before the check-in, they did not sign.

These things never seem to work out well 10 years later when you need them to sign stuff. 

It was easy to sign up with Square.  

I’ve had most luck with signs in front of my plaza and word of mouth - networking at Chamber of Commerce and chatting with other business owners in the area.