Hmmm. Are lands attached to the title in fee-simple or are they allodial?
A small local hex associated with each terrain hex of a Land Grant is apparently allodial. The rest of each terrain hex in a Land Grant is apparently in fee-simple.
What right does the Emperor have to alienate lands without due process?
The Emperor seems to have great latitude regarding the alienation of such lands, but the Noble can always appeal to the Moot. And the Emperor is probably well advised to remain in the good graces of the Moot, which is collectively comprised of all of the Noble Peers.
What are the rules of succession? They seem to vary by title!
They may indeed vary be title, as in some cases inheritance is dictated by local custom. But such details are clearly spelled out in the Patent of Nobility.
If a Duke has 3 children, what SOC are they? 15 or 10 or something in the middle?
Nominally they are 1 SOC-level less than the parent until the heir takes the title and moves up to the higher level. Remember going all the way back to CT it is implied in the SOC stat that all members of a family use titles and are Noble (and thus are effective "Honour Nobility" (- see above) until they inherit), whether they stand to inherit or not. In this way
Traveller Nobility are more like Old European Continental Nobility than the British Peerage. Perhaps a child or heir merely appends the legal honorific "Lord" to their name prior to inheriting, much as the younger sons of Marquesses and Dukes do in Britain. Also, a title-holder might abdicate one of his lesser titles to his heir early (something akin to the modern day British "
Writ of Acceleration", but for a different purpose) in order to grant him experience in administering a holding or to qualify him to hold a certain post requiring a certain standing, prior to inheriting the full set of holdings/grants.
The idea that only the heir is noble (and only upon inheriting) is a peculiarly British notion among the various European peerages that prevented a proliferation of titles among the English. Most European powers considered all children of a noble to be noble, and allowed the children some type of variation in style on the parent's and/or heir's title in common usage (hence the great number of Counts in old Germany and Italy - most were members of non-inheriting cadet lines). ("
Graf Wilhelm von Solcheinland" and "
Wilhelm, Graf von Solcheinland" implied two different family standings socially based on the style and usage - the first was a titleholder, the second was a non-inheriting younger son).
See (Wikipedia):
The Duke holds land from the various intervening titles. Are those titles passed to the oldest only?
Nominally, but there is precedent for dividing some subsidiary titles to different siblings in some cases.
When two nobles of the same rank marry, which titles pass to which offspring? There doesn't seem to be much (any) aggregation of titles over the centuries.
The Emperor may step in and require two or more High Landed Tiltles to be spit among two or more heirs in order to prevent centralization of too much power in a single individual. All titles ultimately derive from the Emperor.