I sent a few emails to his family explaining this, they told me that I was wrong. I gave up and just ignore all of those emails.
It's on gmail and I don't use gmail for important things anyway...
What a bizarre response... somebody who isn't the person you intended to email has replied to you from the address you sent the message to. What could possibly make someone think that the person replying is the one who was wrong?
In their minds, they did email their brother, and the weird guy who replied is wrong. It might be possible, with enough investment of time, to help them understand how/why it went wrong, but as nicolas_t experienced, it is sometimes easier just to block them and move on.
I was lucky, I was a Hotmail early adopter and I regularly receive emails for two namesakes. I was able to figure out their correct email addresses over the years and they are both tech savvy enough to understand the issue. I forward on messages when they come through, and I actually met up with one of them at a house party he was invited to.
When I forwarded the invitation, he suggested coming along as well and I figured why the hell not. It was a fun ice breaker in a room full of strangers.