For at least 20 of those years my parents have been property managers.

This property is a fourplex and the only rental my parent's have owned since 2005.

If you’re okay moving back in with your parents or crashing on a friends couch if it takes longer than expected, then maybe you quit and go full time.I’d definitely build my business faster without commuting back and forth to the pentagon every day.

As a heads-up, my parents haven't lived in the US since 1985.

My parents in law were telling us to go with PennyMac (they're also house hunting for rentals) they were able to get a 30yr for 4.325%.

My other rentals are newer (just over 4 years) and 2 of the current tenants are the initial ones, the other I've had one turnover as the original tenants had to move to take care of a sick parent.

If you have a parent in a nursing home, and can possibly bring them home, do so. 

Horses stashed in the basement are also a problem.And yes, have had both and numerous other hidden pets when there were no-pets policy in place for parents.

For instance, if my parents own a rental property that they want to put in an LLC, can the LLC only include themselves?

Having cash and borrowing from parents are not the same.