Why the answer is 13?
3 4
+.+-+-+-+
| . .1. |
+-+-+-+.+
| .2. . |
+.+.+.+-+
| . | | |
+.+.+-+-+
The second may help the first to come outside through the top wall (1,2), 4 moves, then the first can help from outside the second to move through the bottom wall (7,2), 2 moves.

The first may not go "up" out the top exit because according to the problem statement they must remain in rooms sharing walls/corners on every move.