I want to gain control of all the baronies in my home county. I seem to remember in a previous game using my Chancellor to fabricate a claim on a barony in one of my own counties to do just this, and thereby avoid the revoke title penalty.
In my current game, I've had my Chancellor fabricating claims on my home county for decades without success, despite it saying I have something like a 19% chance of success. Are there any preconditions that might prevent being able to fabricate claims on one's own barons? I have the revoke title law allowed.
As far as I know, you cannot fabricate claims on baronies, only on counties, duchies, and kingdoms (if you have the Become King ambition). And you'll get penalties for holding baronies other than castles (if feudal), castles and mosques (if Muslim), or castles and cities (if merchant republic).
Your best bet is instead to use Intrigue focus, spy on the baron, and try to find an excuse to imprison him. If you fail to imprison, he'll rebel but he can't actually raise any troops, making it easy to capture his holding and take him prisoner, at which point you can revoke without tyranny. If this doesn't work, you can always just revoke him tyrannically: the opinion malus isn't much and it will wear off over time.
Also, are there any penalties to opinion with allies if one responds to their call to arms but doesn't draft troops in support/shed blood in their war, or conversely bonuses if one does? The same question could be asked about the vassal/liege relationship: if one is a vassal and is called to arms by one's liege but doesn't mobilize any troops, does the liege notice?
(If not, it would be a good inclusion into the game.)
No, and this is the key exploit in the alliance system. The AI will
always summon up every last levy but the player is free to simply accept the call to arms and then never actually participate. The only "penalty" is that you won't get any prestige or piety from war contribution score unless you take part.