That’s weird. Maybe it’s a body chemistry thing? I'm on my 4th pair of TOMS (all different styles) and have never had a problem. The oldest are from 1 1/2 years ago and I still wear them all the time! My latest are the vegan ones, with a cloth insole instead of leather - I wonder if those would work better for you (and your brother). My best friend also has a regular pair a few months old, with no complaints.
You should try contacting them. I had great customer service when I had to call them. (Not b/c of them, I ordered the wrong size.)
BTW, TOMS makes different shoes for the kids depending on their environment. Kids in the Guatemala highlands during the rainy season probably aren't wearing the same little canvas things I've got on right now. They also work with the local schools’ dress codes.