If purchaser sues for partition and claims possession of his share you can exercise your right of preemption under section 4 of partition act
2) Supreme Court in the case of Ghantesher Ghosh v. Madan Mohan Ghosh
and Others, reported in [1996] 11 SCC 446. In this case it has been held
that before Section 4 can be invoked the following conditions must be
fulfilled viz.
(1) A co-owner having undivided share in the family dwelling house
should effect transfer of his undivided interest therein;
(2) The transferee of such undivided interest of the co-owner should be
an outsider or stranger to the family;
(3) Such transferee must sue for partition and separate possession of
the undivided share transferred to him by the co-owner concerned.
(4) As against such a claim of the stranger transferee, any member of
the family having undivided share in the dwelling house should put forward
his claim of pre-emption by undertaking to buy out the share of such
transferee; and
(5) While accepting such a claim for pre-emption by the existing co-owner
of the dwelling house belonging to the undivided family, the court should
make a valuation of the transferred share belonging to the stranger
transferee and make the claimant co-owner pay the value of the share of the
transferee so as to enable the claimant co-owner to purchase by way of pre-emption
emption the said transferred share of the stranger transferee in the
dwelling house belonging to the undivided family so that the stranger
transferee can have no more claim left for partition and separate
possession of his share in the dwelling house and accordingly can be
effectively denied entry in any part of such family dwelling house.