Taking out a loan to pay down a mortgage
You have the 2 properties, and even though the value of property B is less than the amount you owe on it hopefully you have some equity in propery A. So if you do have enough equity in property A, why don't you just go to the one lender and get both property A and B refinanced under the same mortgage. This way hopefully the combined equity in both properties would be enough to cover the full amount of the loan, and you have the opportunity to refinance at favourable rate and terms. Sounds like you are in the USA with an interest rate of 3.25%, I am in Australia and my mortgage rates are currently between 6.3% to 6.6%.