IF you do, what type of documents do you have in this book?

It all depends on what level of rigor and documentation you guys want or need to be comfortable. 

You also need any documentation of the condition of the apartment when the tenant moved in. 

--What are the typical legal documents and terms that are set in place/signed to protect you? 

I can give it a shot to add it and share it with you if you'd like, but it's far from a professional document. 

I haven't dealt with a seller yet that wasn't appreciative that the buyer was solving their problem of getting the home sold.But, I have met many sellers who waited too late to participate in or complete documentation to process a short sale and lose their opportunity due to foreclosure sale.

Keep these somewhere that they will never be deleted it is one of the best ways to win court...document, document and document again.So in MO we have to provide the tenant a walk through that is scheduled where the tenant can be there if they want to be. 

Just to be sure, use a selling broker who has documented proof of probate sale experience, to make your offer.

Plus if you actually read their legalese documents, there is a lot of CYA saying they can basically disappear and/or go bankrupt and you lose everything.What I do is direct deposit a certain % of every paycheck into an investor account (and the rest into my normal checking).  

Unfortunately in my state you have to be an important person (Politician) or prove to them with documentation that someone attempted to murder you at least 3 times.