@Sandy Uhlmann You don't need to worry about who redeems the lien, as long as it is redeemed by someone. Keep in mind that redemption of a tax lien is simply a paying of the tax debt and removal of the lien from the property. If it is the owner who redeems, that's great because the taxes are paid and the lien is gone. If it is a mortgage lien holder, they get to add the amount paid as an advance to the loan, and that's all. So if the 2nd lien holder redeems, it's good for you because you have preserved your current equity position (not increased the debt via advance), removed the lien from the property, and the taxes have been paid.
With tax liens, the scenario to be concerned about is when they get to be a couple of years old. In the tax lien counties I have dealt with, the holder of the tax lien has the right to foreclose after some period of time, and I think 2 years is common. If that happens your loan could be wiped out in the process. My policy is to bring the taxes current prior to tax lien sale, and if I buy something with a tax lien I redeem it right away. These things carry high interest and that can add up quickly as a senior encumbrance on the property if not dealt with.