1. Legally, a Release /Relinquishment Deed, duly Registered before SRO, "CANNOT" be unilaterally revoked /cancelled, without any exceptions, whatsoever & whichsoever.... more so specifically AFTER a period of Seven years.
2. Apprehensively, the Sisters jointly are on a Arm-Twisting Spree to swindle you off for more money, bringing about what can be unfortunately & typically termed them as Family's Black Sheep.
3. DESPITE above point no. 1, Sister's would be able to revoke /cancel the said Deeds, using many twisted parameters, which would depend on the documents executed etc....
Keep Smiling .... Hemant Agarwal