1. You are entitled to the certified copies of the documents of title of your ancester,
2. Apply for the same in proper way,
3. The partition was conducted by your grandfather around 30 years back and any document, if available of that old period which went unchallenged uptill now, is considered genuine by the Court,
4. The younger son's descendent has recorded the said partition by changing the survey no. for his share of the property,
5. You can apply for the documents he had submitted for changing the said Survey number and making the partition book from where you can acsertain his basis for the claim of his share of the property,
6. If you do not find any loophole in the documents or in the process, do not venture for unnecessary court cases which will be expensive and time wasting.