Suspected forged lease by tenants

[Sam Simon]

Just wanted to see if anyone had additional input or ideas for this seemingly unique situation:

I recently closed on a single family tenant occupied home with long term tenants.  It is not governed by rent control.   The prior owner passed away in his nineties and all properties went to his estate.  Tenants "apparently" had keys to his unit and no documents were found on any of his Los Angeles properties. 

The tenants provided a 5 year lease with absurdly low rent, signed 7 months prior to his death from a long bout of cancer (with live in care).  It's a scan of a scan and has the relative inconsistencies of a cut and paste.  I purchased the property at a discount due to the 3.5+ years left on the lease and considered waiting things out but the story just doesn't line up... 

Why would a savvy RE investor in his final days write a 5 year lease for one property that reduces rental income and/or the ability to sell for his sole heir?   I was informed that trust documents allowed for the tenants' first right of refusal on purchasing the property at current appraised value...they offered 200k below.  They subsequently turned down a $50k offer to vacate.  They interfered with showings, photos and marketing of the property.  My guess is they assumed they were guaranteeing themselves a steal of a purchase...  

I've consulted an attorney and I'm also reaching out to a forensic document specialist...any other thoughts based on landlord experience?  My first rent check will arrive this week and my plan was to return as to not ratify the lease.