It's not easy to guess what your problem is from such a brief description. If you're talking about AI-controlled workers, the problem is probably that you haven't ticked the "Terraform" box under "AI Strategies". You need to do this so that the AI knows it's a worker. Also, for this to be possible, you need to enable all of the actions under "Worker/Engineer Actions".
Basically, make sure you copy everything from the default Worker, with all the same boxes ticked and so on.
If you run into problems of this kind, it's a good idea to study someone else's mod or scenario to see how they did it.
As for making a scenario with other people's graphics, you do not need consent. People post them here specifically for people to use in this way. However, if you post your scenario on the site, you should give credit to everyone whose work you've used.