Nice Job Konny - I did not know about the revolting part...

It depends on the faction for me, usually it is the king's oldest son, or in some cases his grandson. In one campaign, as Baktria, the king and his sons did not have enough male children, and the only two grandsons of the house of Baktrios were killed in battle. This was absolutely tragic, and I was ashamed of my inability to maintain my proper succession (I tried fertility ancillaries even). I then had to look at the men who married into the family, and more importantly their ethnicity (Persians need not apply...). I decided that I would only consider Hellenes and Makedones for FH. A few years down the line, and my Last Baktrios king is in his late 80's, when one of the great granddaughters marries Alexander Baktrios... Sharp, Charismatic, Vigorous, 16 years old and a Hellen. I role play that this guy is the original king's grand Nephew, and I make him faction heir without losing the original name of my Baktrian Kings.

In My KH campaign I follow a different path. I have three great houses of nobles. The house of Sparta, The house of Rhodes, and the House of Athens. The faction leadership rotates amongst each of these houses based upon my own interpretation of intercine political rivalries. For example, when the original faction leader's son and heir (Spartiate) died, he made a deal so that his son in law would become faction leader, but after him the next faction heir would come from the Rhodes family. The Athenians were opposed to the decision and threatened revolt, but the Faction Leader bought them off by moving the capital to Athens. In the end everyone is happy (The Spartans keep leadership for another generation, Rhodes gets the next faction heir, Athens is in its proper place as leader of Greeks), but in a way that captures the inherent tensions within that particular faction. I may even eventually roleplay a civil war...