Current questions and answers regarding the map editor.

BlockTownGarrisonForAI( 'Castle1', isBlocked )

Instead of isBlocked, it should be true.

DoNotGiveTurnToPlayerAIIfNoTownsandactiveheroes (3, true)

Check the function name (including the capitalization) and the space before the parentheses also seems suspicious. However, I think that in your case, the function will not work, as there are towns. Also, in theory, you can create a battle against neutral heroes using the StartCombat function in scripts, if I'm not mistaken.

To make everything blocked for player 3 when the map starts (slot, race, hero, starting bonus)

This is configured in MapPropretiesTree -> players. Settings for CanBeHumanPlayer and CanBeComputerPlayer.