Procedure for legal heir substitution

Respected Experts My father had filed a partition suit for obtaining part share in his mothers property. he also obtained an order for injunction that his siblings cannot create 3rd party rights till pendency of suit. However he expired on 29th July 2017. We obtained death certificate only a month later. Non advocates told us that "legal heir impleadment" has to be done in 90 days. I made an appearance in the partition suit, where court reprimanded to appear after 90 days due to which perio elapsed, still court has given time to file a detailed application. Other constraint was, my mother did not have any money hence she could not take any steps in several litigations of my father and she suffered weak health too. How do I proceed further. Not getting the right guidance from lawyers as I have been scared that suit has abated. Can I pursue remedy under Order 22 Rule 4 with a delay condonation application for substitution of legal heir with penalty orders of court and delay costs or is there another parallel legal remedy, which a surviving member can take so that suit does not abate. Please guide in the best possible way