Can my mother sell her partition with out consent of sons?

1. Let Mother file "Partition Suit" in the local Civil Court.

Keep Smiling .... Hemant Agarwal
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Her share is yet to be declared and demarcated.

Contact, consult and engage a local prudent lawyer for appreciation of facts/ documents, laws applicable on the subject, professional advise and necessary proceeding.

In whose name the property is now? After your father's demise, whether the property has been transferred to the common ownership of the family including Mother.

In case no settlement deed is made after your Father's death, you may do so now and get it registered. Once it is done, your Mother can do whatever she wants to do with her share of the property.  If the property is still undivided and settlement deed is not made, not only your Mother, none of your family can alienate the property in any manner without the consent of all others.

File a partition suit. Once the property is partitioned, your mother can transfer you her portion without the consent of other brothers. Please consult a lawyer as to which will be more beneficial mode of transfer in that case. 

your mother's share in the property is 1/4 of 3 acres, which is very small portion . Although an undivided share in property can be sold, no one will be ready to purchase it. Hence you may get her share transferred to you by executing release deed in your favor..  

How is that the property is ancestral?