If the NRI is desirous of purchasing the residential property from a resident seller, he may enter into a sale agreement, preferably a registered sale agreement.
Since the NRI is not available in India, he can get the sale agreement entered into through a power of attorney.
There is no such thing called as a memorandum of understanding for purchase of immovable property.
A MOU is not a valid document neither it would be enforceable in law, besides, that also has to be executed by both the parties.
Since the NRI is not in India, he has to execute the same from the country of his residence and his signature has to be attested by a notary public of that country and he may have to send it back to India, which will again be a time consuming factor.,
The buyer should not show haste to buy immovable proeprty especially due to the urgency of the seller.
The documents have to be scrutinized, a legal opinion has to be formed by an experienced lawyer and other details have to be advised by the lawyer besides recommendations to buy the property.
All such things are not overnight story, hence do not be in a hurry or do not have to oblige the seller.
He may be in urgent need of funds, it does not means that he will sell the proeprty with defects without allowing the buyer to become aware of the defects.
If the seller is finding some other buyer, ask him to proceed and do not allow him to dictate terms to you for any reason.