Termination of sevices of old employees having fake certificate .

I am a manager in Uttarakhand Transport Corporation .Recently a employee was terminated by me due to fake intermediate certificate from bogus board .He was on probation and on process of verification his ceritificate was found fake. Later on i came to know that there are 5 employees having certificate from same fake board and served more than 20 years .I am new to this organisation .I came to know that due to corrupt officers in the past ,cerificates of these 5 eployees were not verified and they kept doing their service and even got promotion.The problem before me is that above terminated employee is demanding information of intermediate qualification of above 5 doubtfull employee through RTI to strengthen his case in the court. My questions in this regard are as follows: 1)Should I take action against above 5 doubtfull employees also wthout considering their long service years? 2) If i dont take action against above 5 doubtfull employees ,Will that terminated employee get favour in the court on the basis of above 5 doubtfull employees having fake certificate and serving the organisation for several years ?,