Did verbal settlements can be challenged after 50-60years

Dear Sir/Madam Please note the following Person have 4 son & 2 daughters in early 50's (today youngest son age is 72y) Owner , 3 sons & 1 daughter died only 1 son & 1 daughter is alive Owner distributed his property verbally between his sons in early 50's-60's as it was granted that time. He was living with his youngest son (alive 72y) till his death in 1973 and did not made any will. His youngest son (alive 72y) shifted his residence in 1985 nearby and the said property was locked since. Now the grand son and sons of the eldest son of the deceased owner (as said) demanding their share in the said property. My questions are: 1- Did they are legally be a share holder? 2- Did all 6 children of the deceased owner (as said) is the legal heir and share holders including daughters born before 2005? 3- What to do in case where daughter and son-in law of the deceased owner (as said) are dead, who will legally appear on their behalf. 4- Whether RD (Relinquishment Deed) can be made to settle this dispute and what will be legal formalities. 5- Did verbal settlements can be challenged after 50-60years of the physical possession of the said property.