Lets say he wants 10% Interest bringing the total to $55k and to offer another $5k up front to sweeten the deal. 

You might want to consider sweetening the pot to get the bad tenant to move, if they move out immediately. 

A higher interest rate on a lower principal amount can have the same total repayment as a lower interest rate on a higher principal amount and his tax situation will vary even though the same repayment is made which can sweeten the deal for him.If you strike out there, then you can go to a master lease w/option.

I want to see how the deal can be sweetened by seller-financing and would appreciate any help on formulating an offer.

If you fix a few things up to sweeten the deal they’re usually okay with it.

If i can make this work in his favor and sweeten my deal for a win-win it would be appreciated. 

@Austen Sweeten - I agree with Mark.

I figure I can get investors to hold the $4mil for 4 years and I sweeten the pot somehow.

You can sweeten the deal and find out if the landlord is partial to one of the tennants and allow them to stay for another year minimum or something like that.

https://content.govdelivery.com/accounts/KYLOUISVILLE/bulletins/29c3fff?reqfrom=share&fbclid=IwAR3W2XdbJcNanfHKq_RBRo7KgEkwSe1YO9x1gGCARfKoREjXbm2QDc6XgqMThere was such a retraction of inventory once section 8 tig...