thewanderingknight
Sergeant
BorialisAurora said:
You don't become a Master of the order being in the army as a soldier, you need to leave the army first and then offer vassalage to the Grandmaster, with your rep he should accept and give you land and that's it.
As said in the description (and actually in game in "Game Concepts") there are a couple towns that trying to land will not do anything, all you need to do is to do that on the nearest castle instead.