You are not Attila the hun, and neither are you Mary Poppins. I imagine it is tough being a step mom on top of everything else. You already tried yelling, nagging, and stamping your boot around without much response. I'm thinking your also stressed with clutter and the house not being "perfect" either.
I'm gong to send you to a website that might sound strange to you, but there is much more to it than meets the eye. You could say cleaning and organization is only the tip of the ice berg. She has many not only with cleaning, but mental attitudes, and bringing peace in their lives with one step at a time.
www.flylady.com
Now that said, have you tried the incentive approach? This works depending on what their incentives would be, and if it would be in your budget. You could possibly make a deal with them. If you do this, this, and that and I have a good report for your father when he comes home, then we can do this. Whatever the incentive is, can either be done when your hubby is home, or after he leaves again depending on exactly how much time he has and if he is up to doing anything.
The incentive doesn't have to be an activity, but maybe also a music CD or something they have been wanting. The key would be not to cave in when they do misbehave.
Also, make sure you acknowledge them when they do things on their own that you have been hounding them to do.
PS. With the fly lady, I have heard numerous testimonals that after some of the mothers started "flying", that the kids started to follow their mother's lead after awhile. It wasen't just the younger kids, but the older teens also.