Alan starts with curtain 1 (I'm using numbers for the curtains to avoid possible confusion between C for car and C for the third curtain.)
If curtain 1 contains the Goat, he chooses curtain 3; else he chooses curtain 2. He sees the capitalized items in the six equally likely arrangements below:
Note that in two of his successes, the keys are behind the second door, so you might suspect (correctly) that 2 is a good starting place for Becky. If she does not find the keys behind curtain 2, the other two cases where Alan succeeded are cgk and kcg, so selection of curtain 2 points her to the keys--she chooses curtain 3 if she sees the Goat behind 2, else she chooses curtain 1.
So they win 2/3 of the time.