preaching, stealth and sieging forts
 

I searched, but couldn't find the answer to this one.

1. If I have a unit with stealth preaching in a province where I am besieging a fort, will that unit participate in the battle resulting from an army in a neighboring province attacking?

I know that if I have a unit with stealth preaching in a province that I own, that unit will participate in the defense of the province (unless that province contains a fort, in which case the preaching unit sits inside the fort).

Re: preaching, stealth and sieging forts
 

In my experience, it depends on whether the unit was already stealth-preaching
before your army besieged the fort. I do not think that an unit that starts
preaching in a province owned by you is considered hidden.

Re: preaching, stealth and sieging forts
 

I seem to recall pressing "preach" and first pressing "hide", then "preach" have different effects. The first would have you just preaching, the later stealth-preaching. I haven't tried this myself, but it could work.