I would try not to tie up any of the principal in down payments.Personally, I had a family member do this same thing, but they used an investment portfolio as the collateral instead of real estate.If you play your cards right, this might be the only short-term money you ever need.Please let us know what you end up doing.

They look at your credit profile and get you business lines of credit and credit cards.

With your experience and possible skillset, perhaps finding a company to sponsor you for a green card may be a better option? 

I'm 53, married with 2 kids less than 17 years old with debt only from purchases on credit cards and my home.

Should We:Sell, take advantage of the capital gains law, move, and pay the mortgage off on the new house, credit cards, etc…?

I have two banks that have done so as well as a credit card, and know of a couple of organizations that have as well.

Of course credit card is going to be like 3.5% but it does kind of such because it's already hard to get tenants to pay it lol. 

What about Debit Cards attached to a checking account?

Similar to a credit card.

If you have a credit card with a high limit or a line of credit on the existing duplex that might give you some wiggle room.