PTCL act 1978 - reclaim petition by original grantee

Dear Sir, In 1993 my dad (non SC/ST) had purchased the land (60x40) from an owner (again, non-SC/ST) who had bought it before from a PTCL (Prohibition of Transfer of Certain Lands) act grantee (SC). My dad was unaware of this act (obviously, this is not an excuse) during the purchase. Eventually when my dad came to know about this controversial property, he sold the land to someone else (1995). Since then, this land has been sold and changed hands several times (about 10+ different people). Now, the grandson of original grantee wants his land back for which he has sent a notice to all those who were involved in purchasing this land. As far as I read from the internet about the PTCL act, the selling and purchasing of this grant land is null and void - and hence, the current owner seems to be in a big trouble. My question is, does this affect my dad in any way? Since we were neither the first buyer nor the current owner, we have no connection to this land at this point of time. However, I am worried about the legal implications (long-fought trials - ever dragging adjourns, legal fee if any etc..). Could you please help me with the implications of this case to my dad? Thanks and Regards, Vik