Your uncle can submit an affidavit for name clarification, stating both the nickname (used in property records) and his real name (as per Aadhaar and other ID proofs), confirming they refer to the same person. Along with this, he should provide supporting documents like electricity/property tax bills and ID proof showing matching DoB and surname. This affidavit, along with a name verification certificate from a gazetted officer or notary, should be submitted to DDA while applying for freehold conversion.