I can see it from his perspective of going from paying $0 in rent to paying $X is rough, but I certainly don't want to get into a negotiation after closing with the son.My question is - I got the inspection back and plan on making some requests anyways -  should I / can I require that I have a signed lease from the son before closing? 

Do CODE VIOLATION SEARCH.9Calculate MAX Bid PriceOnce the properties are filtered with the above criteria, set the max bid price between 60% and 75% of Fair Market Value or ARV10Bid StrategyDetermine the low starting and maximum bidding amount, to be agreed by GENERAL PARTNERS11BiddingEnsure 5% of max bid price is in County bidding bank account 3 days prior to bidding12Property Win BidEnsure funds are wired to County bank within 24 hours of WIN13Send File to Lawyer/Title SearchIf property is still occupied, have Legal file a “Writ of Possession” to get former owner removed, Perform Extensive Title Review, Negotiate any existing Liens14Receive TitleReceipt of Certificate of Purchase, Certificate of Title to occur within 3-4 weeks from date of winning Bid, continue follow up with County until received

Don't be afraid to negotiate!

You can ask the owner to give notice to some or all of the tenants during the inspection contingency negotiations.

If nothing else, an inspection report is a negotiating tool.

Expect that anything you tell them they'll tell the owner (which could affect your negotiating position).

I know he's open to negotiation but at this point my eyes are starting to cross running the numbers over and over again while changing the variables. 

It's up to that seller to offer to pay whatever he wants and if that buyers realtor didn't have to split with a sellers realtor he'd have likely done it for 2-3%People act like this stuff is set in stone and there is no negotiating. 

The negotiations get a little harder when you are dealing with a listed property. 

Re-negotiate the agreement if at all possible.