Decree against dead person

A Title Suit was filed in 1998 with the prime accused as Defendant 1 and his wife and children (minors then) as other defendants. Defendant 1 died in 2001 and the Court was duly informed with a petition for substitution of deceased defendant with heirs (already on record as Defendants 2,3,and 4). However Court gave a money decree in 2008 asking Defendant 1 to pay by mistake. Execution suit was filed in 2010 as advised by the Advocate. We have been throughout misguided by the Advocates. As we learn now, the decree was against a dead person and was therefore a nullity though our Advocates made us believe then that the words Defendant 1 to pay in the decree will pose no problem since other defendants were already on record. The Advocate is presently requesting for substitution before the Executing Court u/s 152 of CPC, but we genuinely feel that he is again misguiding us. The question is : 1. Where do we stand now? 2. What's the correct legal procedure under the circumstances? 3. Can the Executing Court allow for substitution? 4. Is the case time-barred for amendment of decree? Pls. help