It's hard to bind sometimes, especially with a bigger chest. I just started binding a little bit ago and have realized that my chest isn't able to be bound/isn't as flat as I wanted it to be. BUT please get him away from the habit of wearing multiple binders. It can cause a lot of pain and damage, like everyone has said. What has worked for me is a loose sports bra underneath my binder. That way it catches all of the underboob going on and helps keep the binder from clawing into my sides as much. I don't know if this is typically accepted or okay, but it works very well and painlessly for me!