1. Could anything have been done to improve the construction of boats in the home Castle?

Yes. After any of the boats on the map disappeared, it was possible to build a boat. There was a limit on the maximum number of boats.

2. Was there a third part of Anduran on the map?

Yes, one of the drowned men had it in the southwest.

3. Why wasn't the presence of artifacts with heroes in prisons displayed in the map editor, and how was this achieved?

The idea to give artifacts to the heroes in prisons came after the save was generated. Since doing this with the editor and then regenerating the save so that all the necessary spells, skills, etc., would appear was very time-consuming, the decision was made to insert them directly into the save. Anduran was needed on that map to collect skeletons from one of the heroes. But getting him wasn't that easy.