If a conventional loan is only available in your personal names, transferring the lot from the LLC to yourselves before the exchange could trigger IRS scrutiny and potentially invalidate the 1031 exchange due to the same taxpayer rule.

They were rehab properties so I purchased under a construction loan.  

Having your son involved in the loan, title, and insurance policy does have both benefits and drawbacks.

I did all of my loans with small local banks in my area and was always happy with the rates and service.

(note that there are seasoning periods with loans - shorter with DSCR loans, and longer with conventional. 

Hard Money loans have been the downfall of many new investors. 

Lenders assume more risk with a higher loan-to-value, so to compensate they'll charge more in points, loan level price adjustments, etc. 

Questions are what type of loan are you targeting?

You might also consider private money loans, local lenders and so forth.

@George Blower  Are you sure on the part that you can't take another 401k loan until 12 months after the first loan is repaid?