Before changing the narration, optative sentences are first converted to assertive sentences.
The woman said, "All travellers are welcome for the sake of one." "Who is that one," said the king, "for whose sake you make all travellers welcome?" "It is our lawful king, Robert the Bruce,", said the old woman.

Explanation

The woman told the king that all travellers are welcome for the sake of one. The king asked the woman who that one was for whose sake she made all travellers welcome. To this the old woman replied that is was their, lawful king. Robert the Bruce.