No matter how well you restrict them, allowing players to have characters in two different realms will always lead to trouble.
Sure, the odd player can pull this off and play both separately and equally different, but the vast majority of players will favor one character over the other. Human nature.
There are likely some that could play their newly developed infiltrator character that comes along and kills their other longtime family member from another realm, but there are not many.
I may be willing/happy to assassinate your longtime favorite hero character, but I would certainly think twice about killing my own.
If you think that allowing a second character in a second realm access to classes like Aristocrat/Diplomat, Aristocrat/Trader, or a religious variation can not adversely affect that second realm, you are dreaming. Diplomats, priests and traders CAN, very much, affect a realm. Normally, quite quietly and unnoticed until the damage is done and it is too late to stop them.
Allowing a second noble in the same realm limited to the (reduced) warrior class is more realistic and practical.
This game is set in a feudal society, after all, family was important. Rather, it was that these characters were eerie, in a roleplaying sense. Consistently inconsistent. And most of all, when something happened to the "main" character (wound, death, capture, etc.), these guys would just pick things up where the other guy left off. This was both bad for immersion and for making these mechanics meaningful.
Absolutely. In most feudal societies the first born or remaining eldest was the one that both decided and spoke for the family.
When the eldest died, the next eldest would normally step up to that position of authority for the family. Even if only temporarily (and limited) to fill in for a wounded or imprisoned elder.
It would be the younger that would more likely be sent off to serve the military while the eldest would take care of family concerns.
Allowing a second noble that must belong to the same realm addresses none of that. However, adding a new class of characters that's excluded from realm chat and titles, THAT bypasses those issues completely.
Allowing the second noble in the same realm allows for larger mobile armies and addresses the cross-realm spying/cheating because both members of the family share the same/similar concerns. I understand that not every family member will always agree or necessarily have the same views on all things, but the game does allow room for roleplaying things like this.
Ultimately the family is the most important thing. If the younger member decides that they do not like their lot in life, they will normally seek to "take control" of the family rather than to just abandon their family and move on.
Excluding characters from the realm chat and titles does little to prevent spying/cheating or other abuse.
Adventurers already have these and many more restrictions placed upon them and yet some players have found ways to work around them and abuse the class.
Giving players access to things like diplomacy, trading and courtier positions, in a second realm, is just inviting trouble.
Again, human nature.
