You can't really judge that by seeing someone on screen, because you only see proportions, not height. For example, Dan Henderson's height is listed at 6'1", and was probably cutting at least 20 lbs to 185 lbs - I doubt your brother looks like him and is the same height at 160 lbs without a cut. Then it's a question of muscle density etc.
I always thought Alexander Karelin looked like he weighed 86 or 96 kg at most (but way shorter than he is), it's only when he stands next to these fat 135 kg dudes that you realize the guy was actually cutting 10 kg to 135, stands at 6'4" and has 20" calves. He had very unusual proportions for a superheavy.
