Sale of property on relinquishmnet deed which was supposed to be built in collaboration.

Let me explain my scenario in detail. My grandfather let's call them HK collaborated with a builder let's say SP to build 4 floors + parking. The property was Freehold under HK's name. Now, during the construction period, HK deceased and a relinquishment deed was made under his Wife i.e IJ (my grandmother). Within a month of relinquishment deed, a sale deed for the 1st floor was made between IJ and a third person say PJ. Now, in that sale deed, it's mentioned that PJ was the builder and he is buying this floor but, the actual builder is SP as per the collaboration agreement with HK. After this sale deed, the actual builder i.e SP stopped giving us rent which was agreed upon and started using pathetic quality material. He even left a lot of items which were agreed upon. Soon after the completion, my father ie MJ filed a case in consumer court against SP (actual builder) & PJ (who bought 1st floor and shown as a builder) for 1000000 (harassment + damages + items left + poor quality material). Question1: Is our case genuine, is there any chances to win? Question 2: My father (MJ) along with 3 others are now the legal heir of the property since IJ under which the relinquishment deed was made is deceased. All the other 3 heirs now want to do registry of their floor on their name but MJ is telling them to wait until this case is over. Should we wait for the case over or proceed with the registry of every floor? Any help is much appreciated! Thank you.