I had a partnership with eight partners. As each one died, his or her heir got stepped-up basis on the value of their partnership interest at the time of death. By the time the last one died, there were eight partners including a trust with 12 beneficiaries! Actually, by the time I inherited this return, several partners had already died and basis had never been adjusted. Nothing had been sold, and there were always profits, so no returns had to be fixed. I spent a great deal of time making spreadsheets to calculate the correct basis for each partner. That's what you'll have to do. Make sure you charge for it! (Alas, in my case, our firm had handled this partnership so it was our fault that basis had never had been reconfigured, so I couldn't add a couple of thou to my fee.)