What type of mortgage?

[Cathy Malmrose]

What kind of solution would you use for this scenario? I think I need a mortgage that allows for 2 separate borrowers? 

Buyer 1 is ready to buy his first home. Salary allows him to get a $340k conventional. No downpayment yet. 

Buyer 2 is ready to sell his $220k home, currently owns it outright but is self-employed, small but sustainable income from investments. $220 will be his cash contribution to the home. No mortgage. 

Buyer 3 (me) has $1.5m in real estate holdings, mostly land contracts, that Net $7k/mo. I have $250k liquid. I don't want to get a mortgage but I can probably get another $250k in mortgage. 

House will be approx $650-750k  in South Jordan, UT. Buyer 1 & 2 are brothers with a long track record of working together well. Buyer 3 is me and while I wouldn't live in the house, I need a place for my 2 youngest to live while in college. A mortgage would be $2k/mo. Dorm rent is $2k/mo. I would rather invest in a home than toss money on rent. The area where the house is located is well-built out and about as stable as a RE market can be. 

Most of my question is in the timing -- The $340 from Buyer 1 can be available in a few weeks, depending on how long the mortgage process takes since it will be his first house. The $250 from Buyer 3 (me) is already liquid, just need to transfer to a single acct ready to go. The $220 from Buyer 2 won't be liquid until his house sells, probably fast but I never like counting on it, so, I am considering a mortgage to cover the gap while Buyer 2's house sells. What kind of mortgage should I get? A 5 yr balloon? Are there any other options for investors like me who have a portfolio but no W2? I am a sole-member LLC.