Hello Sir,
You cannot keep the funds in a NRO Account. You will have to shift the funds into a Capital Gain Tax Saving Account till the time you buy another property.
Please not that the funds are to be transferred before the due date of filing of returns.
If your mother is also an NRI, then the buyer will have to deduct 20.6% as TDS. In case you do not want the TDS to be deducted then you may have to apply for a Lower Deduction Certificate to the Income tax authorities.
Trust this clarifies your query.
Feel free to call / get back in case of further clarifications.
Thanking You.
Regards,
Rohit R Sharma
BCOM, ACA, LLB-GEN, CERT. FAFP