Ancestral property belongs equally to all the share holders and it cannot be sold without the consent of all of them. You may attempt to find out the relevant deeds in respect of this property from the office of registrar. A carefully directed title search can dig out documents even as old as a century. Once you have these documents in your possession you may then immediately file a case for partition to cull out your share from these properties. Get in touch with a lawyer to chart out your further legal recourse.
A case for forgery cannot be filed in such circumstances. No forgery has been committed by those who sold the property. As a share holder it was your duty to be vigilant and take all the necessary legal steps to stop the other share holders from selling this property. Your failure to stop them does not make them liable for forgery in any manner. The legal meaning of expression 'forgery' is way different from the meaning that is ascribed to it common parlance.