If you are U.S. citizens, you would income tax on any gain you enjoyed for the property. To calculate the gain, you have to know the cost basis of the property. It may not be easy to find that cost number.
You may also owe income tax to the country where the property is located. And, depending on how the money is delivered to you, you may be obliged to file federal forms related to foreign bank accounts.
Since the dollar amount is large, you would do well to hire a tax expert to help you. Find one who has handled many international tax questions, ideally some of them involving the country where your property is located.
