Paying zakaat but having a joint liability to pay off

So if I or we are not qualified to pay zakat due to loan not paid off yet. So my question is that for how long we are not going to pay zakat, until we have paid off the loan. As I have mentioned above that it might take long and we do not know when the flat would be sold so in this case if might take years also. It means that until we do not pay off the loan we will not be allowed to pay zakat and do qurbani. So we have to wait all those years for the flat to be sold off and the pay back the loan and then will we qualify to pay zakat etc.
Please shed some light as we are in confusion.
Jazzk Allah Khair!