How often do tenants on month to month need to resign lease?

I think they're justified, and I'm committed to helping them because this seems unfair, but I've never had to enforce the lease except for non-payment of rent.

In the last 10 years we've signed 1500 leases and only had two evictions- those two evictions took between 4-6 weeks from start to finish. 

You should have provided a new lease when you took over.  

Directly investing in real property investments, whether property, notes, tax liens, or leases requires a THOROUGH understanding of all LEGAL aspects concerning real estate law in general and the investment in particular.It’s IMPOSSIBLE for someone who hasn’t accumulated either a legal education in real estate law or 20 years active experience to have the knowledge and understanding of legal aspects sufficient to reduce legal risk to an acceptable level when investing directly in tax liens, notes or real property.  

A Quad is still better due to the fact that you have 4 leases and 4 rents coming in and still can get a conventional loan. 

LTR or Mid-Term RentalIf STR doesn’t work out, consider mid-term rentals targeting professionals, which could offer higher rents and more stability than long-term leases.3.

I use the work tenant is quotations, because the lease was not signed with an individual, but rather a LLC for a property management company who subleased the home on AirBnb. 

Do I need to draft a new lease with the tenant, or can I continue with the existing one?

Scrub their PM agreement, lease agreement, etc.