Unfortunately the tax liens have to be paid before the house can be sold.
I am not a lawyer and I would certainly talk to one. Specifically, the seller was under contract to sell the home to you. They can be sued for non-performance where you can recoup any lost costs. The problem is two fold. One it is probably more money than can be done in small claims court and two it is hard to get money from someone who doesn't have any. The questions to ask is how much money do you need to spend to try and get some money from the seller and what is the likeliness you will actually get it.
Again, I am not at attorney and you should definitely speak to one.... more