Do we consider an ally's castles as "our own"?
If one player has built GM5, can the second player use a DD scroll?
And another question. Suppose we are playing against a brown Barbarian and a red Castle. The Barbarian has built 2xGM3. Can the brown player use a TP scroll? Can the red player use a TP scroll?
In theory, if we consider an ally's castles as "our own", then GM4 must be built in the Castle to use the scroll, which means both the Barbarian and the Castle are out of luck. If we consider an ally's castles as "not our own", then the brown player can use TP, but the red one cannot.
How should one act in such a situation?