You don't know for sure how the other TLs brother has been able to get this information, it could be a copy sent to him by the TL, or could have been verbally given by the TL (less likely that he would remember it word for word), ultimately if the fired TL gave out the info that's done with now as they can't be fired twice, it's about you and moving you forward. If you're part of an investigation you should be, in theory not always practice, protected from any detriment because of your involvement - which is what you say you are suffering now.
If you've been keeping notes (if not, you should be) of what was said, when it was said, and the impact it has on you for example how you feel, how your colleagues behave towards you, etc. then you could file a grievance of your own against the TLs brother. What he is doing is unacceptable from a business process point of view and most definitely a professional one.
Depending on company policy you might be able to raise this as a Whistle-blowing case as confidential, private information has been disclosed to other colleagues, and (in my opinion) gross misconduct (not covered by whistle-blowing) is being performed by the TL's brother as he is taking away your dignity at work - you'd need to refer to your internal procedures to see about this.
If you do take it formally in a grievance, then you could also ask something like "If I my case was to be looked at externally, do you think that the business has done everything it can to protect me from detriment due to my involvement in the previous grievance?" That question, or similar, will get HR thinking and it leads me onto my next point...
IANAL, but you may also have grounds for taking this to an employment tribunal based on not being protected by the business. To me, based just on the information you've provided, there does appear to be a breach of confidentiality and you're now suffering because of it. The business has a duty of care towards you, and if they're failing in that they will need to look into it. If they don't - or it isn't adequate - then you may take this external to your company. However, before you could do that you'll have to follow company policies to try and resolve it which will involve a grievance, and if that doesn't resolve it then an appeal then involving ACAS to mediate.