No

a coparcener cannot make a gift of his undivided interest in the coparcenary property without the prior consent of all other coparceners. Such a gift would be considered void and invalid.

Dear Client, 

It is possible for a coparcener to give up their portion of the joint family estate. A coparcener may give his whole undivided interest to another coparcener or coparceners, and such a gift may be deemed legal whether given with the permission of one or more parties or as a renunciation in favour of all. Renunciation accepted as long as you continue to give him upkeep. However, a coparcener's gift or renunciation of his share in favour of another coparcener or of multiple coparceners is void.

1. The coparceners have equal right on the property of your late grand father which is yet to be divided and demarcated.

2. Any of the above coparceners can transfer the title of his/her undivided share of the said property in favour of any other coparcener or any other person as per law.

- As per law, after the demise of your grandfather intestate , his property would be devolved upon all his legal heirs equally i.e. each will have 1/5th share in the property 

- Further, any of the legal heir can release his respective share in favor of other without getting the consent of other legal heirs. 

- However, as the property is undivided and the patta is also in the name of grandfather , it means that there is no partition of the property has taken place 

- Hence, that alienation is invalid without the demarcation and partition of the property 

First of all grandfather's self acquired property is not ancestral property hence the legal heirs are not coparceners but they are co-sharers.

All the shareholders have equal rights in the property hence if one of the shareholders decide to alienate his or her share share in the property in favor of a chosen shareholder, there is no legal infirmity in it. If the shareholder has executed a registered release deed without mentioning to who she or he has released her share in the undivided property, then her share of property will devolve equally on all other shareholders and not a particular shareholder.

You have not mentioned that how  and by what mode that your paternal aunt has released her share in the undivided property.

You can challenge the same in court it’s illegal and fraud played upon court