At age 16, going through all that those years entail, my wife also tried that crap with our son thinking that if she shoved WT material down his throat by making him read books an answer questions to her satisfaction that he'd do better. It was making them both miserable.
I am pretty sure that this is what is going to happen with what is going on, he is already complaining.
While the dynamics of your situation differ in that he's a "stepson", I'd probably suggest that you ensure that you're available as a sounding board for his frustrations as there will be many to come.
I am trying to be the sounding board......he really does not know what he believes, but he has no interest or respect towards the WTS and really just views them as a 'strange organization'. His memories of past WTS stuff is boredom at meetings when his mom made him go, attending assemblies with his uncle (who is his age) and running around and trying to avoid any of the event. When he sees them go door to door he thinks it makes no sense, and my concern is she will use this, thinking it is going to help, and drive a wedge between the two of them....