What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

If you do not have the experience you need the credit, the right deal, and the capital cause chances of you getting max terms on deal 1 are small.I try to explain this to people all the time, it's not just you the borrower, it is the deal too. 

They use credit cards for emergencies (Yeah, right..) 

They have credit scores of 760 and 670 and just moved to the US two years ago.

Portfolio lenders or credit unions may offer flexible refinancing options, while creative financing can improve cash flow.

Our debt include only our primary, the duplex, and credit card $3,175.91+$7,317.49+$2,000=$12,493.

Now I have equity locked in and couldn’t qualify for a heloc due to credit as well.

Honestly, big banks have terrible rates on mortgage.Work with a broker, they are your best bet; pricing beats big banks 9 times out of 10.

., if 20% down payment in purchase agreement, have him place all those funds in escrow at the settlement company with clearly written signed addendum that should buyer not close by x date for any reason, those funds are nonrefundable and to be released to you, but all credited to buyer at settlement if they close.

Do some banks or credit unions let you refinance at 90% LTV?