Time limit to challenge for right if land is one person’s name since 30 years

Sir , One farm was a joined property of five brothers. In 1974 the heirs of five brothers given powers of dividing land to two arbitrators and they have clearly stated on the stamp paper Of Rs 50 , that they will accept what arbitrators decision and all have trust in them. It was given decesion that the land of 5 acres to be sold at Rs 25000, which is market price. And any one brother or anyone (but first preference to family members )can purchase who can pay Rs 25000. Everybody had signed appointing of arbitation. Desesion was accepted but one of the brother’s signature was not done and it was overlooked as it was not noticed, the son of the brother paid to all five brother or their heirs Rs 5000x 5 times .The land was transfered on the the name of the purchaser the next week in 1974 after giving statement by all brother and Mamlatdar order on the joint statement in written.None of the brother till their death appealed or challenged in the court distribution of land but after 15 years of the death of one of the brother, in 2015 the heirs of one of the brother went to the court stating that his father had told them he has not accepted decesion so they are claiming 1/5 part that is 1 acre of land as prices of land had hiked by the time.The arbitration was on legal stamp paper duly signed by all four brothers and one bother’s heirs who was not alive in 1974. It was family understating and it was done willingly appointed arbitrators by all party concern . It was in good trust not registered as it was family member’s deal.amicablly accepted but till the death of all five brother none of them had appealled or challenged that he is not accepting the arbitrator’s decesion or say Lavad . This land is in Gujarat state. The money paid by the arbitator was mentioned that they have paid Rs. 5000 to all five brothers and their heirs and receipt was given to the purchaser. Now after 40 years the purchaser could not fine all receipts. Two are lost during this time. The purchaser heir could not trace but he could produced affidavite of one of the arbitator who was alive in 1995 that money was paid to all five brothers personally and receipt was handed over to the purchaser. Both arbitrators also has died by 2015. I would like to know is it there is any time limit for challenging and arbitrators decesion after certain years . Till today none of heirs of other four brothers has apealled . Please advise what possible decesion can be in this case. Thanks