Also Seller hasn’t paid property taxes in 2 years which is a sign the property is in distress.

If someone has been given POA maybe they could sign it.

Put it in writing and have both of you sign it.

You just need basic documentation, such as the NIF (Tax Identification Number) of your company if it’s already registered, and they usually take care of the rest.I recommend, Jesús, that before signing up for a virtual office, you first establish your company (SL) and officially register it.

I am considering doing this but should I charge a fee to write up and get the lease addendum signed?

It's difficult to see how a tenant will be after screened and signing a lease.

I've obsessively been listening to every podcast episode I can, reading all the books, and signing up for any and every workshop and educational seminar.

Before you sign anything, definitley pin down the timeline for permitting and building.

And, they all sign the lease. 

I am now currently a Superhost my first Airbnb has over 50+, 5-star reviews!!!