They probably wont tell you at this time, because you haven't sold it, because it could be years before you got a buyer so the figure they give you now would be wrong, what would normally happen is your lawyer would approach the town hall as part of the litigation once the sale is going thru.
As for renting it you would be liable to pay tax on the income and also non residence tax.
Spain unfortunately is a night mare of red tape, and they change the rules to suit.
I am sorry you lost your parents in such and awful way.