Lizards in general are more complicated to keep than snakes. Iguanas are famous for having a Metabolic Bone Disease that is caused by nutritional problems. This is most likely what happened to your brother’s iguana. It causes deformities and death.
Lizards require ultraviolet light. They require calcium supplements, vitamin and mineral supplements. They require both vegetable matter as well as insects to eat. I think most people that buy a cheap iguana don’t know what they are getting into. Unfortunately, it’s the iguana that pays the price.
Snakes of the other hand get all the nutrition they need from their prey. In the wild they live healthy lives eating only rodents. That is easy for us to duplicate in captivity.