Colleagues threatening to file false complaint. How to save ourself?

You can file a complaint with the Police whereby intimating the police that you are being threatened of false implication by your colleague in false case under the stipulated Act.

In addition - you can register a complaint in the Police Station for Criminal Intimidation and threat under Section 506 of the Indian Penal Code.

Section 503 defines Criminal Intimidation as “Whoever threatens another with any injury to his person, reputation or property, or to  the  person  or  reputation  of  any  one  in  whom  that  person  is  interested,  with intent to cause alarm to that person, or to cause that  person to do any act which he is not legally bound to do, or to omit to do any act which that person is legally entitled  to  do,  as  the  means  of  avoiding  the  execution of  such  threat,  commits criminal intimidation.

As you have stated that they are threatening you to file such false complaints and lower your reputation and harass you, this shall be covered within criminal intimidation.