Your cousin has no share in property 

once gift deed is executed duly stamped and registered your mother would be absolute owner of property 

3) on mother demise , you would be absolute owner of property as your father per deceased you and you don’t have any other siblings 

Dear client,

Notorised adoption is not valid and by virtue of gift deed, your mother is absolute owner. Cousin has no claim.

If the grandmother made the transfer by gift to your mom in her lifetime, then the relative has no legal right whatsoever 

Its only when your grandmother would have died without making any Will, can in such a situation the legal heirs would be entitled to make a claim

On the registration of gift deed in favour of your mother, she becomes its absolute owner

They have no right in the property as the same is gifted to mother ,through registered deed and she is absolute owner of the property.

1)once gift is made and duly stamped and registered made by donor and accepted by donee the gift is complete. Gift Deed cannot be cancelled unless it is a conditional Gift,
2)The title to the property passes on the done donee is absolute owner of property. 

3) gift deed was made by fraud, undue influence etc., then they can move court to challenge the revocation of gift deed. 

1. The property stands in the name of your mother by virtue of the gift deed registered by your Dadi

2. She is the owner of the said property as per law.

They do not have any share in the property and any claim by them is not legal. 

the same becomes the self acquired property of your mother. 

they will have to challenge the gift deed to claim the share, which will not be possible at this stage. 

Do not worry 

Send them a legal notice if they create unnecessary pressure upon you. 

Regards  

1. Was it your grandmother's self acquired property? If yes, she had full legal competence to gift it to anyone she desired. When a gift deed is executed it results in an instantaneous transfer of title from donor to donee whereupon donor ceases to have any right, title or interest in the property. 

2. Unless your grandmother lacked competence to executed the gift deed or the gift deed executed in favour of your mother is conditional she is the absolute owner of the property. 

You can refuse to give them let them file proceedings and take

If the property was transferred to your mother by a registered gift deed then their claim is not maintainable.

You can remain silent or ask them approach court for relief.

1. As per the information mentioned in the present query, makes it clear that your mother got the property from your daadi and it’s makes more Cristal clear that the nature of the property was self acquired as per the Hindu slaw of Inheritance because the same was inherited from a women but not from a male ancestor. 
2. And also even if it had been come to your mother by dada then also it would have been the self acquired property subject to the condition that dada did not receive the property from his Male ancestor.
3. The gift deed has already been executed giving the property to your mother by dadi, so according to the law in force, no body can claim anything from the property in question as your dadi had all right to give the same to anyone and she did that by gifting it to your mother.