Hello, we paid interest to our mortgage holders in 2016. We paid it to a loan institution that held the papers on their property. We don't have their ssn or ein

Your seller needs your info to file their taxes as well, so this be a good time to exchange information. But in case you still can't get your seller's info, you’ll have to print out and mail in your return with an attachment explaining why you can’t provide your seller’s tax ID.  I suggest you contact the mortgage holder and get their tax ID number.