There is plenty to do for people who can't ride at all. Some of the roads up there are roads the company I worked for built to get rigs up to drill gas wells. You'll see people driving stock pickups on the main road up there occasionally. The real ass puckering stuff you have to make a conscious decision to go do. There's no point where the trail just turns into something ridiculous out of nowhere. I'd feel confident taking little kids on 50s to Brimstone and having a good time.
It's up to debate if there is anything at Brimstone tougher than anything at Windrock but having been to Windrock I think you'll find Brimstone much more enjoyable and your kidneys and butt will thank you. It's a lot less rocky so you'll find yourself going up dirt trails instead of stairstep rocks all day.