There are a number of solutions for this issue. I would suggest different things for different ages and specific issues.
For all ages i would suggest openDNS where you can filter web content across your network.
www.opendns.com
For ages 3-12 I would suggest KidZui. I'll disclose that I do work for the company but its a great product. It's a web browser for kids. Your step son can play his games as usual in a safe environment. KidZui allows kids to explore the web in a fun and safe way.
www.kidzui.com
As far as rearrainging the house, its worth thinking about, as nothing replaces parental involvement. But remmeber the goal is to teach your step son to use the internet resposibly so vary the level of independance based on performance.
let me know if you have any comments about it!
owen dot west at kidzui dot com