Newbie redeveloper DD

[Matt W.]

Hey everybody, I'm looking for advice about redevelopment play. It involves two adjacent lots on a busy road right near my neighborhood. Both lots have small, run down houses on them, and I believe at least one has renters. I saw a handmade "for rent" sign and called the owner. I spoke to a woman who helps her older father manage the properties, and she says he wants to get out of the game.My question is how to structure the contract so as to give me plenty of time to make sure I can redevelop it in a way that makes sense? I already have spoken with a very experienced redevelopment specialist, and a big local builder/investor that have been very helpful, but they will only work with me so much until I have a property under contract.  I also don't want to waste their time on hypothetical deals. 

 My thinking is, assuming there is a tenant lease that must be honored, say at least 6 months, that should be plenty of due diligence time to hire the development specialist and make sure the project makes sense. I think I should give minimal or no due diligence/earnest money so I can walk away if it doesn't look worth it. Any advice is appreciated!