I think its best to try and find a local bank or credit union to finance this. 

Get that low down payment and he can start building credit.

It might also be worth looking into establishing a line of credit for future flips, so you have quick access to funds without needing to rely on third-party lenders all the time.If you're interested in exploring more financing options or ways to streamline future projects, feel free to reach out.Best,Drago

The applicant has solid credit score of 750+ and has a good household income as well.

Local Credit unions and small regional banks.  

Thanks Ned, Short answer to explain it, I did not know they were around back then, just found out now when we are coming back, a little background, when I started in 2005, I was a child :) 28 years old and thought I knew it all, all, all :), did not know about hard money lending, only new about bank loans, and Home equity lines of credit, did not know where to find more money, since I did not have much, I would rely on what I could get from banks, loans, credit cards and was not always that great, it was a learning experience.....and Wholesalers, I did not know that even existed, everything I would find back then was already on the market and through a "friend" agent, MLS, FMLS and all those, nothing like what we have today.

My credit score is 640 and DTI is 27%.

Based on what you've shared, here are some options to consider:Leverage Home Equity – Use a Home Equity Line of Credit (HELOC) or refinance to access funds for a down payment on an investment property.House Hack with a Duplex – Sell your home and buy a duplex.

Your lender will likely base the loan off just one income/credit though (at least that's how my lenders have done it)I would personally advise against it - life is a windy road and you never know when one of you may want out of the deal even if both have full intent to stay in from the onset.

., but it does make things much easier AND give you access too a wide range of benefits, not the least of which is obtaining your SSN and being able to build U.S. credit and access financing.