But if you have the cash or can pull it from another account or can get a gift for the down payment.

My knowledge in that area is virtually non-existent.

(Even went beyond the second page of Google.)I have an investor who wants to partner on a deal by providing a loan for the down payment.

You are bold for taking on a non-paying tenant. 

I have been considering asking to buy the single family in cash to separate the deal but would like that amount to be subtracted from the purchase price while keeping the cash I would spend on the down payment the same to include the single family that way the seller gets the same amount of cash upfront.

Quote from @Jake Handler: For anyone that has been a buyer or seller of a seller finance property, what method of payment and tracking did you use for buyer to pay seller monthly? 

@Nate WilliamsWith one income, two kids, and limited cash flow, minimizing risk is key.

There is no need to remove cash flow now; just keep reinvesting.

Sounds like a cash out refinance would be the best way to tap into that equity. 

I don't see you getting a huge amount of cash out of this property with a new loan, anyway.