Refinance your rentals and reuse the cash.Add a Business HELOC "Line of Credit" on the extra equity. 

I have already run a credit check and everything is essentially perfect. 

I've been researching using Lines of Credit to pay down a mortgage (this one is for my primary home).

If you try to get a HELOC from a mortgage broker the rate will be crap (if they can do it at all), if you try to get a purchase investment property loan from a credit union or big bank then it'll take 4 months just to be declined at the last minute because your CPA didn't dot an i on page 7 of your tax returns, etc etc, you get the idea.

Will she allow you to run her credit?

The is a fee to use a credit card.

I did it... basicallyI took out a line of credit against my home.

The homes will easily pay off the student loans once the house is paid for.I would not put money in stock that might make 7% when I owed 7% in student loans or 21% on credit cards.

@Nick Danaluk - The homestead aka STAR credit received in NY does not make your taxes go up faster. 

I'd call local banks and credit unions, ask for a mortgage specialist, and then asked if they refinance investment rental properties, and if so, what the terms are like.