I am just a bit confused with a few domain actions as I read them directly from the original 2nd ed. setting:

Contest action
Can Law regents provide their holding level in a contest action between 2 other regents?

e.g. two guilds contest each other. All regents in the domain can assist anyone with RPs. But who can assist with their holding level?

Rule action
Can a Law regent oppose with his holding level the ruling of a province? Can the province ruler oppose the ruling of any holding (except source ofc) using his Province rating?

And finally. Suppose a province (5) has two Law regents. Both have a Law holding (2). One of the two is the province ruler too. The other one contests the law holding of the ruler. So he must roll d20 and roll over :
10 (Base) + 2 (opponent's Law) - 2 (his Law) + 5 (opponent's province rating) = 15 ?