Pagdi system flats are governed by the Maharashtra Rent Control Act, 1999.
The tenant does not own the flat – ownership remains with the landlord.

The tenant only has tenancy rights, though those rights are heritable.
On death of a tenant, tenancy rights devolve upon certain family members residing with him at the time of death (spouse, children, etc.), under Section 7(15)(d) of the Act.
If only your maternal uncle continued living there, he may have become the de facto tenant in practice, but legally the rights did not automatically extinguish the rights of your mother (his sister).
If rent receipts were never transferred to his name, and your mother’s consent was not taken, the legality of his “exclusive” redevelopment agreement is questionable.
If the builder attached rent receipts in your grandfather’s name (not your uncle’s), that strengthens your case that tenancy was never transferred exclusively to your uncle.
If your uncle was not the sole lawful tenant, he could not will away the entire tenancy/redevelopment flat.
Under Hindu Succession Act + Maharashtra Rent Control Act, your mother being a Class I heir of your grandfather has a claim in the tenancy rights.
Since tenancy was not formally transferred solely to your uncle, your mother can challenge the redevelopment agreement.
She can demand her share in the redeveloped flat or compensation.
File a suit in the Small Causes Court (Rent Act jurisdiction in Mumbai) or City Civil Court, seeking:
Declaration that your mother is a legal heir of the original tenant.
Injunction restraining builder/uncle’s family from excluding her.
Partition of tenancy rights in redeveloped flat or equivalent compensation.

Was your mother staying in flat on her father demise kindly clarify 

2) under provisions of  Section 7(15)(d) of MRCA upon the death of a tenant, the tenancy passes on to a member of tenant's family who has been residing with the deceased tenant or operating the premises for commercial purposes at the time of his death. The legal heirs come into the picture only when such a member is not available, and the same is decided by the Court as to who is to be treated as a tenant.

3) your mother is st liberty to claim share in redeveloped flat 

Your  mother is at liberty to claim share in said flat 

Your mother can file a suit for declaration of legal heir to the original tenant. 

An application can be filed in the same suit for injunction against her brother and the builder from excluding her in the redevelopment process as a legal heir to her deceased father. 

If her oral request to include her name in the property is declined or not entertained then she can issue a legal notice demanding her inhertance rights in the pagdi system property after which she can approach court of law for relief and remedy. 

Your mother can claim rights in the pagdi flat and the redeveloped property under the Hindu Succession Act and the Maharashtra Rent Control Act (Pagdi system), subject to certain conditions.

Under the Hindu Succession Act (amended in 2005), daughters have equal inheritance rights as sons, regardless of whether they were living in the property at the time of the original tenant’s death. This means your mother, though married and not residing in the flat at your grandfather’s death, can be a legal heir and claim her share in the inherited property.

Regarding the pagdi system in Maharashtra (including Mumbai), tenancy rights generally transfer to the legal heirs who were residing with the tenant at the time of their death. However, possession or residence is a key factor in tenancy rights under the Maharashtra Rent Control Act, 1999. Despite this, the amendment and recent interpretations have supported daughters’ rights, and holding documents like your mother’s election card linked with the flat address strengthens her claim. The builder’s attachment of your mother’s name in election lists shows recognition of her as an occupant or legal heir.

The tripartite redevelopment agreement signed by your maternal uncle in 2019 and the subsequent delay in transferring rent receipts and property documents complicate the matter, but do not override the inheritance rights of your mother as a legal heir. The fact that the rent receipts were still in your grandfather’s name and not transferred to your uncle or mother indicates that formal mutation or recognition of tenancy rights to heirs is pending, which your mother can legally pursue.

Your mother can file a suit for declaration of title, ownership, and partition under the Hindu Succession Act asserting her legal heirship and claim her share in the redeveloped flat. She can also seek a direction for mutation and transfer of tenancy rights in her name and an injunction against demolition, possession transfer, or sale to others without recognizing her rights.

To summarize:

• Under Hindu Succession Act (2005 amendment), your mother has legal heirship rights irrespective of residence at your grandfather’s death.

• Under Maharashtra’s Pagdi system and Rent Control Act, tenancy rights typically require proof of residence at death but daughters’ inheritance rights are recognized judicially and legislatively.

• Your mother’s election card and attached documents linking her to the flat strengthen her claim.

• She can legally file a suit for declaration, partition, mutation, and possession in the redeveloped property.

• The suit can challenge the builder’s unilateral agreements or possession ignoring her rightful share.

As it’s a tenancy property for seeking tenancy rights the legal heir has to stay with the deceased tenant 

Based on Maharashtra property law, the mother has strong legal grounds to challenge the redevelopment agreement and claim her rightful share.

Key Legal Issues

Invalid Agreement: The 2019 redevelopment agreement is legally questionable since the uncle had no valid succession rights to the pagdi tenancy.

Succession Rights: Under Hindu Succession Act 2005, the mother has equal inheritance rights as a daughter, but pagdi tenancy has specific residence requirements.

Legal Remedies Available

Civil Suit for Declaration

File suit seeking:

• Declaration of mother's legal heir status

• Setting aside the 2019 redevelopment agreement as void

• Claim for proportionate share in redeveloped property

Key Evidence Supporting Mother's Case

Strong Points:

• Election card with pagdi house address proves legal connection

• Uncle's unauthorized document transfers without legal succession

• Rent receipts still in grandfather's name till agreement proves no proper succession

Residence Requirement Challenge

Under Section 7(15)(d) Maharashtra Rent Control Act, tenancy rights typically pass to family members residing with tenant at death.

Counter-argument: Mother's election card at pagdi address and continuing legal connection may establish constructive residence.

Recommended Action

1. File civil suit immediately challenging redevelopment agreement validity

2. Seek interim relief to prevent further possession transfer

3. Claim equal share under Hindu Succession Act with evidence of legal connection

Success likelihood: Moderate to high, given documented legal connection and questionable succession by uncle.

your mother is married and upon her marriage she moved to her matrimonial house

so she has lost tenancy right in her father's pagdi property

it seems your uncle was living with your GF when he died

that is why the builder executed the agreement for the new flat with your uncle

it does not matter if the rent receipt still stands in the name of your GF

Hindu succession act and its amendment in 2005 does not apply in case of succession to pugdi properties

for tenanted properties the mode of succession is provided in s.7(15)(d) of the rent act

as per above provision upon the demise of the tenant the family member living with the tenant succeeds to the tenancy and only if there was no such family member would the legal heir of the deceased tenant come in the picture

if your mother seeks a declaration that she too is entitled to the tenanted house she will not succeed due to the definition of tenant given in rent act and for the reason that she is married and thus lost her right in her father's tenanted property 

Yes, your mother can claim her share in the redeveloped house, since tenancy rights devolve on all legal heirs under Hindu Succession Act read with Rent Control Act. She can file a civil suit and/or approach Rent Controller to establish her co-tenancy rights. Your uncle’s agreement and will cannot override her share.