Do you own the 3-family in your own name or in an LLC?

If neither wants to sell you may consider putting everything into a jointly owned LLC with governing documents spelling all of this out. 

I have a 2, LLC's that own each other.

How does the transaction work between me personally and my holding company LLC?

LLC/ Corporation documentation (Must be a US based corporation or LLC) Most lenders may require a minimum credit score of 650 for this program if the borrower has US credit. 

@Andrew Watson I have a similar setup - One series LLC to One bank account.

Purchase price: $2,900,000 Country Glamping and Development LLC acquired 776 acres for a project called Country Glamping on the River, LLC.This is Rawland/Off-Grid/Glamping/STR and Owner Financing for Lot Owners that want an Oasis Get-A-Way and Glamping ROI development on the TN River.you can see the Project: www.CountryGlampingontheRiver.com What made you interested in investing in this type of deal?

Buyer is a newly formed LLC out of Houston, so even farther away.  

AHP Servicing LLCAllied ServicingAngel Oak Evergreen Note ServicingFay Servicing LLCFCI Lender ServicesLand Home FinancialMadison Management Services, LLC National Asset Mortgage, LLCNote Servicing CenterHome Key ServicingMIGSuperior Loan ServiceingAllied Servicing CorporationUnited Home Loan Services Inc.

It's always best to have  multi-member LLC.