I want to note first of all that I'm most familiar with the FS noble system, and will be the basis for my discussion. As ColBosch noted earlier, things are rather different in the DC, CC, and FWL, so my remarks probably aren't all that applicable there.
First we need to make a seperation between "Mechwarrior families", whose title would be baronet at the most, but more likely some knighthood, and "Noble families" with military traditions which would be a Baron and above.
As knights, the title isn't inherited, each generation has to prove himself worthy of renewing their title. Losing the title, would hurt the entire famliy. Choosing the best successor helps the entire family, including the child that get passed over, since he can still attend a national Academy or simply hang around the family estate like he's in "Downtown Abbey".
Among noble families, whose inheritance is already secured, and battlemech forces likely to be at least a company and more, actually piloting the battlemechs is more of a privileage than a duty. Their main role is to actualy financialy support the formation for the planetary/national needs, their liege don't really care what's the individual mechwarriors last name is.
Fair points. I think it could be broken down even further. Here's how I would (and I'll use these terms in the rest of the post):
Very High Nobles: These are your House Lords, their immediate family, March Lords, important state ministers (head of MIIO, for exampje). These folks are so high that they break all the rules and we probably shouldn't try to draw generally-applicable paradigms from them. Unfortunately, they're also the folks we know the most about, so I'll likely end up making some references to them anyway.
High Nobles: Dukes and Marquesses. These people have major administrative responsibilities over entire worlds or more, and likely own the fealty of dozens to hundreds of lower-ranking nobles.
Low Nobles: Counts and Barons: These have some administrative responsibilities, but are lower on the chain, closer to the people, and a few might even be elected by the people instead of inherited offices.
Knights: Just barely nobles, they can't mete out justice, collect taxes, or the like, and are generally noblity in name only. Likely to include many up-jumped commoners. I'm not sure that Knightly appointments are generally for life only, though. Where are you getting that? I haven't seen anything indicating that they are generally any different from other noble titles, which are generally hereditary unless specified otherwise.
It's pretty difficult to effectively administer your fief when you're on your second consecutive year of a military campaign into the draconis combine. Do you believe nobles on the front lines spend their days pouring over financial reports? This is only strenghen the point of the person managing the estate at home, and the person fighting on the front line to be seperate people...
It depends on the administartion. For Knights, who have no power over the citizenry and can't collect taxes, you're likely right. They can hire someone to manage their estate in their absence. There are probably a good number of absentee knights, though I'd imagine that if they don't ever put in an appearance there might be some social pressure from their noble superior.
For higher ranking nobles, I think it's going to be different. If your noble title includes responsibility to rule, mete out justice, hear complaints against your noble subordinates, and the like, you're probably better off staying close at hand. A Count who isn't around to hear complaints against corrupt barons might find himself subject to a citizen-prompted Public Inquiry by his own superior. Even so, they have few enough responsibilities they might be able to foist them off on someone else, likely family or subordinate nobles, but I doubt you can just hire some administrator when your job may include stripping lesser nobles of their titles. I can only imagine how badly it'd go if some commoner filling in for an absent Count tried to relieve a Baron of his title. If you're a Marquess or above, the multiplying responsibilities probably make it next to impossible to spend much time away from your fief.
It also depends on where you're at. Deep in the interior of the Crucis March, it might be easier. Out on the borders, if you're away playing soldier and aren't there to direct the defense when your world gets raided, your boss is probably going to take it out of your hide.
The "Family", the Legacy, comes first. BT has examples of nobles assassinating their children if they feel they're jeporadizing the line; giving the battlemech to someone more competent to act as "champion" of the famliy, is tame by comparisson. It also isn't stripping their inheritance, it's securing it.
Among noble famliies? Yes, very much. That's established in cannon. Even if not inheriting their ancestral land, they still have a good of being appointed to rule a portion of it, or even assigned to different lands through political means in order to expand the greater famliy power.
That never stopped anyone...
This is where you lose me. What indication do we have that in BT society the extended family comes before the immediate family? None, so far as I can see. Parents are going to look after their own children before they take care of nephews, nieces, cousins, etc. That's simply human nature. A parent doesn't secure anything for their children by giving the mech and title to their 2nd cousin. Hell, that's a good way to end up like Harrison Davion, when you tell your kid they're not getting anything but some money and an apartment in the mansion, while cousin Bob's getting the whole estate and the mech. Maybe children get disinherited occasionally, but it's not standard to pass the lion's share of the inheritance to the extended family's best mechwarrior, regardless of degreee of consanguinity. That doesn't make any sense.
Really? Because it's EXTREMELY common in BT... I suggest pouring over the handbooks again. Each nation has at least one planet devoted to nobles who don't won't to actually live on their crummy dirtball, just cash their checks, and do their political machinations if they're especially industrious.
Julian is the lord of Markeson. When was the last time he even visited there? A decade or more?
Saying to your lord "I'm a stupid warrior who can't do math, so I ran the place into the ground, but at least I fight good" is much more likely to get your estate stripped than appointing a proffessional.
Well, I have to go to work. Disscuss.
Maybe knights can get away with that. But if you have a duty to rule, oversee lesser nobles, the planet's defense, etc? If you're abrogating all that responsibility to serve in a regiment somewhere, why shouldn't your noble superior take the title from you and give it to the hireling who's actually doing the job you were appointed to do?
Julian's one of those cases that's so high the rules quit applying. Almost everyone on the Privy Council is going to have one or more noble titles. None of them are actually doing that job, because the Prince appointed them to a post on New Avalon that's more important. He probably has some Marquess overseeing the world and only contacting him if something goes seriously pear-shaped.
Something else that's barely been touched on but has relevance is BT lifespans. Most House Lords don't live that long for a variety of reasons, but every indication is that most people, especially on worlds with good tech, live well into their 80s, 90s, even beyond. It's very possible that the average heir in the IS can spend 40 years in the military, then retire to play with his grandkids and study under mom or dad for another decade before they actually assume their post. Actual nobles might generally be in their 60s, 70s, or even older when they take over (though there will of course be exceptions). By that age, the military would probably rather they retire anyway. It's probably a lot easier for the noble to decide what part of his duties to focus on He's 102 and has been retired from the AFFS for 40 years, his heir is 80 and overseeing the Planetary Guard while he waits on dad to die, his heir is 55 and contemplating retirement from his post as a colonel in the AFFS, and
his heir is 32 and busily trying to advance his career, while teaching his own 10 year old the rudiments of mech piloting....