Why does Moses encourages Alice, his wife, and son to run away?

Moses believes Caldonia is in love with him and will free him so that they can be married. Moses knows he must get his wife and child out of the way so that he will be free for this marriage. Moses tells Alice that he wants her to take his wife and son to safety and that he will join them later. Alice suspects Moses is setting them up, but she agrees, as does his wife and son.