Tragic Glass: Age and treachery… asks the question about the importance of birth order. Good question.
I have never made much of birth order—except in my pre-historic Amber game “The Bloody Grievance“. Even there, I created a short list of pre-gen characters for players who wouldn’t have had time to do their homework for the con—and then allowed Players to add to it.
Sometimes Players filled in the gaps I’d left between “3rd eldest” and “7th eldest” and sometimes it didn’t seem to matter to them.
I think it would matter if two things were played out.
1. Older scions get an insight into the younger ones basic foundation. The way they were treated, the friends they had, the things they had trouble learning. This GM-only work should count in game.
2. GM might hand out “trophies” in linear style from eldest to youngest.
eldest: 4 trophy
next: 3 trophy
next: 2 trophy
youngest: 1 trophy
No trophies overlap. All are unique. They can be made into a pile of such things—and can be discussed with the PC concept in mind.
So Benedict might get:
eldest: fast draw; top secret passages; god of archery; flowering staff
and each of these things means something sticky in the game. Something others might want but not be able to have.