Since the XYZ has already transferred her share of property in the complex to her granddaughter, now the granddaughter is the absolute owner with clear and marketable title to the property.

She only has to execute the registered sale deed in favor of the prospective buyer (provided she is major by age or her guardian has to execute the same after obtaining permission from court).

Besides these details, you may obtain a legal opinion from a local lawyer before venturing into the purchase of this property.

Once gift deed is executed duly stamped and registered grand daughter is absolute owner of property 

she is free to sell the property 

you can ask her father to be witness for sale deed 

Check the following  the documents before purchase…

1. Original sale deed in favor of seller by builder to XYZ. (if sale deed is available, the risk of bank loan of property ruled out)
2. Original sale deeds of seller’s seller and linking documents.
3. Municipal records, as to whether property is mutated in seller’s name.
4. Clearance of municipal dues, electricity dues, water cess, telephone dues.
5. Approved sanction plan.
6. A public notice to be issued seeking objections by unknowns to purchase of property.
7. Circle rate of property for payment of stamp duty.
8. Obtain consent from husband of seller and take signatures of sellers of sons and daughters if any.
9. Obtain consent NOC affidavit from XYZ.

For further clarification you may contact me through pathlegal. Hit the like button if the advice is useful to you.  

Dear Sir,

1. Since the property has been gifted to XYZ's granddaughter, you need to buy the property from the granddaughter.

2. You will need to verify the following documents: 

• Copy of the sale deed through which the seller got his title to the property

• Copies of all earlier sale deeds to verify the chain of past owners of the property

• Registration details of the sale deed

• Agreement to sell the property

• Receipts of payments made by purchaser to seller

3. The buyer has to upload all the documents online on the portal, before visiting the sub-registrar’s office for sale deed registration. The documents required are:

• Original documents, with the signature of all parties.
• Encumbrance certificate.
• Demand draft/bank challan of payment of full stamp duty.
• Property card
• Section 32A photo form of executants and witnesses.
• Identity proof of the buyer, seller and witnesses.
• PAN card.
• Power of attorney.
• Aadhaar card.
• Address proof of the buyer and seller.
• Photograph of the property’s exterior.
• Pattadar passbook for agricultural land.

4. You will also need 2 witnesses to validate the sale registration

Thank you 

God bless

- Since XYZ has gifted the property to the grand daughter , then this gift deed is legal and cannot be challenged, and she is having her right to transfer /sell that property to you. 

- You should check the ownership of XYZ  with the society papers in their name

- Better take assistance from a local lawyer at the time of registration and for checking the papers.