Would denouncing cheaters from an exam make me less likely to receive penalties?
Talk to someone you can trust.

The rules in your place seem to be very severe. Therefore, I advice you not only to listen to people in this forum, but to consult someone who knows the rules in your country. In my other answer, I recommended ombudswomen/ombudsmen or the student union. As in your country, you can be banned from higher education for 5 years, I would advise you to talk to a lawyer. Let them advise you.

In most places, the best way would be to "confess". However, if in your place it is possible to get punished for five years for what you did (which is in my eyes no misdeed at all, as you did not know you helped cheaters) there may be more messed up rules/strange things going on. So please, for your own sake, consult a lawyer (or similar), good luck!

(And yes, of course consult the institution rules and try to find out if similar cases happend before.)