I think you have been given good advise. Brothers want to talk to you? Well don't they have your number? Why are they calling you?
Don't run from it. Just play dumb.
We want to meet with you. Why? No thank you. If they insist, ask if this is a committee issue and what the charge is. If it then comes out that you were having dinner with a disfellowshipped relative, you should ask directly who reported it. Once again, this takes place before you say it did or did not happen. this is important, because it gets them to admit and name a person spying on you during lunch, and reveals the fact that they did not follow Matthew 18.
Ask them directly, if they told this person to come to you directly in the spirit of Matthew 18.
At that point you can say, well guys, it was a business lunch and nothing spiritual was discussed, so you can lower the flag and relax. I won't be discussing it, but rest assured I was not in deriliction of the direction. You brothers however could have avoided this by having this person reach out to me directly like the scriptures clearly lay out. Why would you not do that?
then thats it.