As long as the purpose of the secession isn't to shorten the refit route, and as long as there's a decent IC reason for the capital location, then you won't run into trouble with titans for the secession.
What Garas say about Brock that he known Brock wish to create a new realm for quite sometime. Sometimes he know a bit too much. Coupled with former Xavax nobles wish for a new realm, my character is fulfilling many characters wishes including Brock himself IC.
If Highmarch is a long time realm in planning, I think Brock suggested new realm will be much older if not same age as the Highmarch idea itself.
But I really do not know if I am correct to understand as I do now, and furthermore I do not wish to assume that everything is in order.
This. The rules basically boil down to "don't cheat and don't ruin the game for other people" - in a player driven game like this it's impossible to do anything other than look at complaints on a case-by-case basis.
What if this new realm somehow gives OI realm a room to grow? If new realm absorb OI, that is 3 duchies. Thinking about it, Brock has IC reason to fulfill to a Duke wishes to play a greater role in this island. Even without OI lands, that is 2 duchies, giving new realm a good stable realm size. More than that number regions for a new realm in Slimbar or same number but better richer regions... If with OI, they get 3 duchies, good size for realm and can play better role in this island too.