NOC from mother & daughter in favour of son (Notarized and this has not much legal value). As the property is based in Ghaziabad, UP, so relinquishment deed or gift deed doesn't seem to be an option as those don't get registered in Ghaziabad. Release deed is an option but that involves paying some percentage of property as registration amount.
Mere NOC or an unregistered relinquishment deed shall not transfer the rights of the sharer to the co-sharer.
The registered release deed relinquishing their rights by the mother and sister in favor of the son shall be the legal and proper transfer to hold him having marketable title to sell the property.
Though the registered transfer involves stamp duty and registration charges, this cannot be avoided since this is the correct legal option under this circumstance.
Seller wanted to avoid going for release deed from mother & sister and wants to directly go for Sale Deed which gets executed by all the three (son + mother + sister). Is that fine or something else needs to get done?
The seller may be having plenty of such useless ad illegal ideas because it is not he going to face the problem at a later stage bcause he will not be available to solve this problem, it will become a burden to the buyer.
Dont go by the seller's false words.
You may face property disputes at a later stage in any form hence insist on registered release deed from the legal heirs in favor of the person who would be selling this property