Work it into the day, go to a park for a picnic, a ballgame, some outing everyone likes. If you ride in drops, consider a city bike or citifying a mountain bike so you can ride in a slower, conversational manner. Start small. Build up to hills on your routes. Switch an errand to bike based, library, video store, coffee, whatever. Do the heavy hauling on the errand. Go at the pace of the slowest and don't push them to go faster. Take breaks often. Make sure all the bikes are comfortable and in good condition.
With younger kids look at a tag along to get them pedaling without major effort.
Basically make it easy, relaxed and fun. If you bike regularly, your ease with traffic and on the bike can be intimidating to a non rider. You want to do everything possible to minimize that. Show that biking is a normal, easy activity and you're making a more even playing field. Upright riding positions, platform pedals and normal clothes go a long way towards making people more comfortable on bikes and making cycling approachable. If you live on busy streets, consider taking the bikes to a park or path as cars add distraction and fear. Giving too much advice too early can be bad too.
My wife didn't ride till recently and it has been much slower going than I'd like, but we're making progress. It took a while to get her comfortable on the bike. It's taking longer to figure out how she likes to ride. We got a ex-rental bike that I fixed up to just get her on a bike. Now that she's been riding a year, we're looking at other options. But simple things like how to get on the bike, when to shift etc had a much higher learning curve than I expected. If you explain something, giving the reasoning behind it helps and only working on one thing per ride helps too.