Encouragement is the key. Read books to your children that illustrate the steps of using the potty. Reward them when they even get one of the steps right. You have to make potty training fun rather than a task. Young children respond to positive reinforcement when taking on new adventures.
You might want to "divide and conquer:" choose the most advanced child or the "lead" child and get him/her trained. Then the other will likely follow along. Remember that stressing over this will not help even though you have reason to be stressed.